If you are interested in plant galls, you'll know how important it is to correctly identify the host plant as there is often a high degree of specificity between the gall host and the gall causer which makes identification a lot easier. It's not always that straightforward however, as I discovered when I found galls on the leaves of a Mountain (or Alpine) Currant Ribes alpinum.
Galls on a leaf of Ribes alpinum
These are clearly true galls as the red patches are swollen rather than simply being discoloured, and looking Redfern & Shirley (2011) - the standard work on British galls - there are few options on Ribes. In fact, the key quickly moves to an answer, both caused by aphids of the genus Cryptomyzus:
On redcurrant R. rubrum, galls caused by C. ribis which are yellow-green in colour.
On R. alpinum, galls caused by C. korschelti which are pink, orange or reddish.
The plant ID is definitely correct (a known specimen confirmed by an experienced botanist), so it looks like C. korschelti, but it's important to check carefully, so let's see the aphids themselves.
Aphids on the underside of an R. alpinum leaf
Close-up of an aphid on the underside of an R. alpinum leaf
By now you should have seen the difficulty - this is a yellow-green aphid, but this implies the aphids are C. ribis which are not, according to Redfern & Shirley (2011), found on R. alpinum. However, rather than having found a new species, I thought it was more likely that this is R. ribis on an unusual (for the UK) host. However, having consulted with an aphid specialist (thanks Fiona!), not only is it unusual to find Cryptomyzus on the underside of the leaf rather than inside the galls, but the galls themselves are too swollen. So, let's look even more closely...
Siphons (or 'cornicles') at the rear of the aphid's abdomen
Cornicles are an important way to separate some aphid species, and these are broadly swollen with a slightly widened rim at the end (this isn't very clear in the photo, but it is there), the whole being approximately bottle-shaped. In Cryptomyzus, the cornicles are narrower - this is a different genus. Without going into too much detail here, it turns out that (thanks again Fiona) it is in the genus Hyperomyzus, specifically H. lactucae. This is rarely recorded in Britain (though this doesn't necessarily mean it is rare, just that not many people look or can identify them), but it has been found here before and is known from Ribes in continental Europe.
Many galls are not well understood and minor discoveries like this can be made quite readily if care is taken to look, especially given that R. alpinum is not especially common in the UK and probably poorly studied. The lack of readily accessible/affordable identification guides (Blackman & Eastop's 2006 2-volume opus was needed for this species, but is not cheap) makes aphid study more difficult (plus some genera are taxonomically confusing and really require genetic analysis and/or research), but as I found, there are specialists who are ready to help and it's always worth asking. Now to let the authors of the gall key know what I've found, then check whether H. lactucae has been recorded in Hampshire before...
References
Blackman, R.L. & Eastop, V.F. (2006). Aphids on the World's Herbaceous Plants and Shrubs. (2 vols.). Wiley, Chichester.
Redfern, M. & Shirley, P. (2011). British Plant Galls (2nd ed.). FSC, Shrewsbury.
We all like earthworms. Yes, they are slimy and they wriggle, but they mainrtain our soil and allow us to grow food and garden plants. However, how much attention do we really pay to them? Probably not much, hence this post.
The 'common-or-garden' earthworm Lumbricus terrestris (sometimes called the lobworm) is probably the most familiar (it's the one we study at school) and is what is often being considered when we talk about 'earthworms' in a general way. It is the largest red earthworm in the UK and is often found when digging in gardens or grasslands. Although it's also found in orchards, it is less common in woodlands, farmland and near rivers - other species take over in these habitats - and it isn't even our most common species, even if it the most familiar; that honour may go to the 'grey worm' Aporrectodea caliginosa. Britain has around 45 species compared with 180 in France - the English Channel is a real barrier if you can't fly or swim.
Much is written about L. terrestris so I won't repeat it here - instead I want to look at two rather distinctive species. The first of these is the manure worm (AKA brindling or brandling) Eisenia fetida which is up to around 120mm long.
A pair of Eisenia fetida mating
Close-up of the joined clitellum ('saddle') regions of mating Eisenia fetida. Note how the clitellum is wide and almost encircles the other worm.
Reproduction in earthworms is complex and I'm not going into details here (maybe in another post), but E. fetida is an easy species to find and recognise (note the red and pink banding), hence its inclusion here. It is often found under decaying vegetable matter - manure, compost, wet rotting wood, wet leaf-litter and so on. It's also the only British earthworm to be regularly reported indoors - it pretty thin and can squeeze up between cracks in flooring in old, dilapidated buildings and can even be found in drain-traps and the like i.e. wherever it is damp and there's decaying matter to live in.
The second species, the 'green worm' or 'stubby worm' Allolobophora chlorotica is very different.
Allolobophora chlorotica in garden soil.
A. chlorotica is pale (or if darker, it is greenish rather than red), no more than 80mm long (usually less), and often found in the C-shape illustrated here. It's common in gardens, grasslands, woodlands and in/near wetlands and water-bodies - so, if you see something like this, is isn't necessarily a worm you've cut in half while digging.
This has been a very quick look at just two species, but they are both common and distinctive, so I hope you'll look for them as they go about their essential business, and maybe look out for some other species too. Enjoy!
Further reading
There are plenty of gardening and allotment books that talk about earthworms in general, but I think a good one is:
After a bit of a break looking at bees and ladybirds among other things, it's time to return to the topic of taxonomic morphology - how the careful observation of structure allows the identification of species, even if they initially appear difficult or are in unfamiliar groups. The true flies (Diptera) are one group that can be tricky as there are many whole families that are unfamiliar to non-specialists and consist of small unpatterned species. Having collected one such specimen recently, I thought I'd use it as an example of how something that initially looks difficult might not be - if you have the right literature and observe carefully.
Working through the useful (if imperfect - it's not an easy key to write) Unwin (1981), the fly below, which is largely yellow-brown, bristly and about 3mm long (excluding legs & wings) turns out to be a member of the Lonchopteridae. The antennae consist of short broad segments (the 3rd one almost spherical) with a long terminal bristle (arista), and the wings are somewhat elongate and pointed, the veins running largely longitudinally and also being more or less equally thick and evenly separated.
Specimen of Lonchoptera
Now, the family has been determined, it's time to move onto the species-level key of Smith (1969) - there are only a few species of this family in Britain and they all belong to the genus Lonchoptera. Although it's not especially clear here, the middle tibia lacks a 'distal anteroventral' bristle (i.e. a bristle near the base of the tibia, on the front of the underside). Moving on, it is clear that the scutellum (the semicircular structure behind the thorax) is not an intense black colour.
Thorax and scutellum of Lonchoptera. The thorax has two bristles (the bases shown by red arrows) while the wings only have cross-veins near the base (e.g. as inidicated by the black arrow)
From this point, the identification is straightforward - the antennae are dark, indicating this this is L. lutea, a common species across Britain which flies between April and October.
Head of Lonchoptera lutea showing dark antennae (the near-spherical 3rd segment bearing a long arista) and the triangle of orange simple eyes (ocelli) on the top of the head.
So, we have a species-level identification of a small fly - though common it is likely to be missed by many non-specialist recorders and is a good example of a small and initially unremarkable-looking species that can be confidently identified without dissection.
References
Smith, K.G.V. (1969). Diptera: Lonchopteridae. Handbooks for the Identification of British Insects10(2ai): 1-9.
Unwin, D.M. (1981). A key to the families of British Diptera. Field Studies5: 513-553. Available for download here.
Following on from my introduction to 7-spot and harlequin ladybirds, in part 2 I want to look at some other common British species. The next most familiar is probably the 2-spot ladybird which has two common patterns which look like they could be separate species - either red with 2 black spots or (despite the common name) black with 4 or 6 red spots. The 2-spotted form has large white side-spots on the pronotum (a bit like 7-spots and harlequins and this can look like a black M/W mark) but the others have a more or less black pronotum. In all forms, the legs are black. The 2-spot is found on a wide range of plants in many habitats, and is common as a species that over-winters in buildings.
The two common colour forms of the 2-spot ladybird mating on a reedmace
Another common species is the 24-spot which is a rusty orange-red colour with black spots. The exact number of spots varies (from 0 to 24, with 20 being a common number), and they can be fused - there are also darker forms but they are not as common as in the 2-spot. The elytra also have tiny hairs which are visible with a hand lens (and can just be seen in the photo below). This is found in grasslands where it eats leaves and is commonest in the south of Britain.
24-spot ladybird found in loose soil on an ant-nest
Keeping with the black-on-red species, the 11-spot is widespread and common on various plants on dunes and in other habitats. As is often the case with ladybirds, the number of spots varies (from 7 to 11, although 11 is most common) and the pronotum is black with white sides.
11-spot ladybird escaping digging of soil
Superficially similar to the 11-spot, Adonis' ladybird is less common with a more scattered and localised distribution, although it has been spreading recently. It is red with 3-15 black spots (often around 7) and the pronotum is black with variable, but generally more extensive, white edges and marks than the 11-spot (in the photo below you can see that the front edge of the pronotum is white).
Adonis' ladybird on plastic on a farm
Lastly, the kidney-spot ladybird which is scattered but can be locally common, is black with 2 large orange or red spots. It is associated with various deciduous trees, especially willows, poplars, ash and birch, and is usually found at or near the base rather than higher up. The description may sound similar to the dark form of the 2-spot, but these have 4 or 6 red spots whereas kidney-spots have two red spots - this is why scientific names are so useful - common ones can be misleading. Also, the kidney-spot is much rounder when viewed from above and has splayed edges making it look almost tortoise-shaped. In the photo below you can see a yellow fungus growing on the rear of the elytra - if you want to know more about what this turned out to be, have a look here - it was quite surprising.
Kidney-spot ladybird - note the yellow fungus growing at the rear
So, that is 5 more ladybirds covered - don't forget that there are also the yellow-and-black species (they may form the subject of a separate post), plus some striped ones, some rareties and the micro-ladybirds. If this is a subject that interests you, there is a UK Ladybird Survey for all abilities where you can send in records of your sightings which all helps understanding the dynamics and ecology of one of our most popular groups of insects.
Further reading
Majerus, M. & Kearns, P. (1989). Ladybirds. Richmond, Slough. An excellent little book with detailed keys to species, including the 'micros' - a new edition is being prepared.
Majerus, M., Roy, H., Brown, P. & Ware, R. (2006). Guide to Ladybirds of the British Isles. FSC, Preston Montford. A fold-out laminated sheet perfect for beginners.
Roy, H., Brown, P., Frost, R. & Poland, R. (2011). Ladybirds (Coccinellidae) of Britain and Ireland. FSC, Shrewsbury. Details of all species including maps, identification features, ecology and so on.
Common and scientific names of species mentioned here
A few days ago, I asked a question on my Ecology Spot facebook page i.e. whether anyone had any requests for topics they'd like to see. The first one was to cover aspects of identification of more familiar species for non-specialists. This is a slight departure as I often look at the fine 'taxonomic morphology' of more obscure (even if not uncommon) species, but it's a good idea so here goes with the first of what I hope will be an ongoing series, Part 1 of a beginners' guide to ladybirds (or ladybugs if you prefer).
Ladybirds are beetles of the family Coccinellidae, and are often split into the larger and more familar 'macro' ladybirds and the smaller microladybirds or 'inconspicuous' ladybirds. In Britain there are 47 species in total and 26 are the more typical species that I want to look at here (well, a few of them at least). The most familiar is probably the 7-spot ladybird which is large (for a ladybird) and has (on its elytra or 'wing cases') the typical pattern of black spots on a red background. However...
Teneral (recently emerged) specimen of the 7-spot ladybird
This is a 7-spot but is yellowish rather than red as it is a newly emerged adult and its pattern has yet to develop. In fact it you looked even earlier, you'd see this:
A 7-spot ladybird just having emerged from its pupal skin
The reason for showing these pictures, apart from being a reminder that even common things can be tricky, is to show two key features of the 7-spot:
Black legs.
Black pronotum (the plate between the head and wing cases) with white spots to the sides.
Features like this are important as they help distinguish species from each other even when the spot pattern is abnormal (which does happen - spots can be fused, increased in number or missing). There is a Scarce 7-spot which is very similar but has two pairs of tiny white triangles underneath (by the hind and middle legs) while the 7-spot has a single pair (by the middle legs).More commonly however, the 7-spot needs to be distinguished from the Harlequin ladybird.
Harlequin ladybird
The Harlequin is well-known as an invasive non-native species that has spread rapidly across Britain since its arrival from Asia in 2003. It is often found hibernating in buildings and evidence has started to be found of its impact on native species such as the 2-spot, through competition for food and by direct predation of eggs and larvae. The Harlequin is highly variable (see here for the range of patterns) though the one above is commonly seen. You can see that the legs are paler than those of the 7-spot, and the pronotum is more extensively white with a black M (or W) shaped mark. Easy!
That's all I want to cover for now - more coming soon. If this is a subject that interests you, there is a UK Ladybird Survey for all abilities where you can send in records of your sightings which all helps understanding the dynamics and ecology of one of our most popular groups of insects.
Further reading
Majerus, M. & Kearns, P. (1989). Ladybirds. Richmond, Slough. An excellent little book with detailed keys to species, including the 'micros' - a new edition is being prepared.
Majerus, M., Roy, H., Brown, P. & Ware, R. (2006). Guide to Ladybirds of the British Isles. FSC, Preston Montford. A fold-out laminated sheet perfect for beginners.
Roy, H., Brown, P., Frost, R. & Poland, R. (2011). Ladybirds (Coccinellidae) of Britain and Ireland. FSC, Shrewsbury. Details of all species including maps, identification features, ecology and so on.
Common and scientific names of species mentioned here
If you are a regular reader of 'the spot', you'll know that I keep stick insects, and will have seen images of them on their favourite British food, brambles (Rubus fruticosus). Bramble is an excellent plant from an insect-owner's perspective because it is freely available just about anywhere with woodland, hedgerows, rough ground, gardens and so on. It is however a wild plant and therefore occasionally includes other unexpected invertebrates. So, when I found a couple of pupae (AKA chrysalis) while cleaning out one of the cages, I wasn't particularly surprised, but I was intrigued to know what they were. As my stick insects are breeding, I have a container full of eggs and this is where the pupae were put. Shortly afterwards, this is what I found...
Pupal cases after adults have emerged
The pupal case on the left is in dorsal view and shows where the wings developed, plus the split where the adult emerged. You can also see the abdominal segments with rings of small protrusions, plus hooks for attachment at the tip (see below for more detail). The case on the right is in oblique/ventral view and shows where the antennae (note the annulations) and legs developed, as well as again showing the split through which the adult emerged. As these were in a sealed container, albeit with air-holes, it was never going to be tricky to find the adults, and I managed to photograph both of them - micromoths of the family Tortricidae.
One of the emerged adult tortricid moths. Note the darker rear half of the wings with paler curved bars to the sides. Length approx 16mm.
The second tortricid moth, noting the very different wing pattern. Length approx 20mm.
The overall form shows they are in the family Tortricidae, but there was of course no guarantee that they were the same species, especially given how different they look. However, there was clear evidence they were in fact the same species, and indeed different sexes...
Tortricid egg mass
This egg mass, along with several others, was found inside the lid and with no other insects present had to be the product of these moths. The eggs had been laid in moulded fold in the lid just as, when outdoors, they would be laid in shallow folds of the upper surface of leaves and the greenish colour would offer camouflage. A closer look showed the next stage.
Tortricid moth larva
I soon noticed a few tiny, recently hatched larvae, no more than 2-3mm long. The head is to the right (you can see the feeding apparatus as a short dark line) and the segmentation is just visible. By now I had identified the adults as Epiphyas postvittana, the Light Brown Apple Moth; a species with highly variable markings as you can see - more examples are given in Manley (2008). It is a native of Australia, first recorded in Britain in 1936 (possibly as early as 1911), which is now abundant in the south of the country and spreading northwards, aided by its polyphagous diet (i.e. it eats leaves of many plants). This species is also known for its sexual dimorphism - males (the top photo) are smaller with a sharp change in colour across the wings; the larger females are more uniformly coloured as seen in the lower photo (Bradley et al. 1973). In Australia it is a pest of apple orchards (and may well have arrived with imported fruit), but in Britain it feeds on other plants, only eating apple foliage in captivity. So, the title may be a little unfair to this species - its larvae 'devour' no more than any other species, though it is non-native and arguably invasive if it competes with native species for food.
So, an unexpected indoor arrival, but a good opportunity to look at a range of stages of its life cycle - I'll leave you with a few more images of the pupal cases.
The tip of the abdomen of a pupal case of E. postvittana - the hooks (note the curled 'Velcro'-like tips) are used to attach to plants during pupation.
Ventral view of an E. postvittana pupa. The antennae are the clearest elongate structures, while the positions of the legs and mouthparts are also visible.
An example of how much detail can be seen - as well as the fine sculpturing of the surface of the pupa, and the sutures between segments, a spiracle can be seen bottom right.
References
Bradley, J.D., Tremewan, W.G. & Smith, A. (1973). British Tortricoid Moths. Cochylidae and Tortricidae: Tortricinae. Ray Society, London.
Manley, C. (2008). British Moths and Butterflies: A Photographic Guide. A&C Black, London.
Having started to look at identification of spiders, I've been meaning to buy a tuning-fork for some time, and last week I finally remembered to go into a music shop and get one. 'What has a tuning-fork got to do with spiders?' you may ask. Well, for quite some time, it's been known that spiders detect vibrations from their prey, such as insects caught in their webs and from the exact strands that are vibrating know where on the web their potential prey is located. They don't respond to slower taps on their webs as these are far too low a frequency and might be a larger predator hunting them instead. So, if you get a vibrating tuning-fork and touch an occupied spider web, there's a fair chance that the spider will emerge, lured out by the fake meal. Just watch...
I haven't identified the spider, but it looks like one of the several similar species of Tegenaria that inhabit such places - houses, outbuildings, and (as in this case), garden sheds. You can see that it emerges when the vibrating fork touches the web, and immediately attacks the 'prey' (suggesting that vision is less important at this point) - when the fork is removed, the spider returns to its funnel-shaped retreat. This is a good example of this 'trick', but things are rarely as simple as they seem, so what's going on from a biological perspective?
It was way back in the late 19th century when the 'influence of a tuning-fork on the garden spider' was first (as far I am aware) scientifically reported (Boys, 1880). Since then, a considerable amount of research has been undertaken. For example, Parry (1965) investigated the signal that a prey insect generates, noting that previous work had tended to focus on artificial signals similar to the sinusoidal wave generated by a tuning-fork. Tretzel (1961) had already found that prey made higher frequency sounds with a greater range of intensities than young spiders (which were therefore lower-pitched and more even) but was uncertain whether spiders used frequency to differentiate between prey and their own young, though they clearly can differentiate between them in some way; similarly at this time there was a lack of evidence about how spiders differentiated between prey and inanimate objects hitting the web. Taking a more straightforwardly visual approach, Savory (1952) had observed responses of Tegenaria to tuning-forks and found that:
The spider first runs to the fork and try to grasp and bite it (as seen in the video).
If the fork is used repeatedly, the attack reponse ceases as if the spider has learned there is no prey ( I found that the spider in my video only responded twice - the third time it stayed in its retreat).
However, if a fork with a different vibration frequency is used, the attack reponse starts again (if it were a prey insect, there would be a complex range of frequencies of vibration).
Conveniently given the subject of my video, Parry also looked at Tegenaria and found segments of sound that he termed 'fast transients' - essentially parts of the prey insect (legs, antennae) 'plucking' web threads like a guitar string, either by dragging across them or by becoming detached and allowing the thread to snap back into position.
As the spider grips a bundle of threads in the claws of its front legs, these 'plucks', along with high-frequency vibrations are easily transmitted to it from the web. Little more could be concluded but Walcott (1969) investigated the structure of the sensitive receptors on the 'feet' of all eight legs of the house spider Achaearanea tepidariorum. He found a lyriform ('lyre-shaped') sense receptor organ with 10 receptor units, each sharply tuned to particular frequencies between 60 and 1400 Hz, although the sensitivity of each unit depended on the tension of the slits forming the organ (think of it as a 'harp' or 'guitar'-like arrangement). However, it was responsive to air-borne vibrations, not web-borne ones, presumably because the web of this species was a poor transmitter. This arrangement also implies that the 'learning' response that prevents repeated attacks on a fake prey stimulus (if the same frequency of fork is used) is linked to one or a few units being effectively switched off for a period). Later research by Barth & Geethabali (1982) investigated the function of the lyriform organ in more detail and concluded that the units/slits were not tuned to particular frequencies but that there was some difference in the precise response curves that could allow frequency discrimination; they also concluded that vibration sensing was only one function of the lyriform organ and that it might also be involved in proprioception (i.e. the spider's own sense of where its limbs are, just as you know where your arms and legs are when you have your eyes shut). This contradicts Walcott (1969) but this may of course be due to genuine differences between spider species.
Now, I could go on - and indeed much has been written on this subject, but it turns out that the range of responses is highly variable. Different species of spider focus on different frequencies (or ranges of frequency with differing response intensities); the extent to which visual cues are used varies (e.g. in the ogre-faced spiders Deinopsis, the simple eyes are large in order to hunt at night, while some species have reduced eyes), as does the response e.g. the 'attack' seen in the video is common, but a 440 Hz fork (as used above) has been reported as causing the orb-weaver Eriophora sagana to fall from its web in a predator-avoidance response rather than treating the vibrations as prey (e.g. Nakata 2008). This work has indicated that airborne vibrations are used by E. sagana to detect insect predators, and that predation can lead to changes in web structure - thus there is a complex interaction between prey availability (in the sense of web structure being related to prey capture) and predation risk, with vibration detection being a mechanism that at least partly informs this balance.
The upshot of this? Well, first of all there is clearly more to be understood, even with a simple experimental tool such as a tuning-fork. I certainly intend to look at the responses of other spiders such as orb-weavers and jumping spiders. Secondly, I might have to buy a wider range of tuning-forks. Thirdly, if you've tried this, please do leave a comment to say what happened.
References
Barth, F.G. & Geethabali (1982). Spider vibration receptors: Threshold curves of individual slits in the metatarsal lyriform organ. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 148(2): 175-185.
Boys, C.V. (1880). The influence of a tuning-fork on the garden spider. Nature23: 149-150. Nakata, K. (2008). Spiders use airborne cues to respond to flying insect predators by building orb-webs with fewer silk threads and larger silk decorations. Ethology 114: 686-692. Parry, D.A. (1965). The signal generated by an insect in a spider's web. Journal of Experimental Biology 43: 185-192.
Savory, T.H. (1952). The Spider's Web. Warne, London.
Tretzel, E. (1961). Biologie, Okologie und Brutpflege von Coelotes terrestris (Wider) (Araneae, Agelenidae). Teil II : Brutpflege. Z. Morph. Okol. Tiere50: 375-542. Walcott, C. (1969). A spider's vibration receptor: its anatomy and physiology. Amer. Zool.9(1): 133-144.
