Bubble-butts and water-walkers

It's about a month since we lined and filled our garden pond and it took less than 24 hours for the first invertebrates to find and colonise it (they were small Hydrellia flies which formed a breeding swarm within 48 hours). Since then, things have moved on - as covered in a recent post, dragonflies and damselflies have already found it, the large water mint (Mentha aquatica) is proving very popular with nectar-feeders, and a common frog (Rana temporaria) has taken up residence at one end.However, I want to look at a couple of other pond residents - beetles and bugs (that's the Hemiptera or 'true bugs' rather than bugs in the general sense...).

A water beetle Rhantus suturalis on bare new pond-liner - its breathing air-bubble is visible at its rear.

The largest beetle currently present is Rhantus suturalis (photo above) which as about 12mm long excluding appendages - note the 'smudged' dark mark on the centre of the pronotum. This is probably the most widespread water beetle worldwide, being found from northern Britain to New Zealand (Foster & Friday 2011). It tends to be associated with stagnant water in lowland areas, often in newly created or polluted situations - our pond is neither stagnant nor polluted but is certainly new and this beetle appeared within about a week, possibly transferred with water plants. This specimen seems to spend much of its time hiding under the bridge over our pond, but is also seen regularly swimming rapidly around the pond, including visits to the surface where it exposed its rear to replenish the air bubble used for breathing.There are some other small dark water beetles which I have yet to capture and identify (I'm tempted not to disturb the pond much at this early stage), but also beetle larvae.

Beetle larva in side view

Beetle larva in dorsal view

Again, I haven't identified this larva (yet) though it does look like Rhantus, maybe a smallish early stage - time will tell, but there are several which can be seen swimming actively to and from the surface. Meanwhile, up on the surface, taking advantage of surface tension to allow propulsion, pondskaters of the genus Gerris, probably the common pondskater G. lacustris, hunt for prey items that fall into (or rather, onto) the water. This species is well known as an early coloniser of new ponds (Denton 2007) and can be seen skating rapidly towards potential prey which is then pierced with the tubular mouthparts.

A pondskater Gerris lacustris, an early coloniser of new ponds

As well as predation, I have witnessed both reproduction (copulation) and aggression between Gerris. The latter appears to be as a result of encounters between males (some are territorial, actively courting approaching females) which are brief, in the form of immediate attack and retreat. Females also hold territories based on food supply. The sexes signal to each other by making ripples with the legs and abdomen, the frequency indication whether the sender is male or female. Males then judge which it is and act accordingly with 'courtship' or 'repel' signals, though they are not always correct (Savage 1989)!

So, although the pond is unlikely to mature that much more before next spring when the first full plant-growing season starts, an aquatic community is beginning to develop and will undoubtedly feature here from time to time as interesting species and behaviour catch my eye.

'Til then, if you'd like more info about creating a wildlife-friendly garden pond, why not download an advice booklet here (from the excellent Pond Conservation).

References

Denton, J. (2007). Water Bugs and Water Beetles of Surrey. Surrey Wildlife Trust, Woking.
Foster, G.N. & Friday, L.E. (2012). Keys to the adults of water beetles of Britain and Ireland (Part 1) (2nd ed.). Handbooks for the Identification of British Insects 4(5): i-iv, 1-144.
Savage, A.A. (1989). Adults of the British Aquatic Hemiptera Heteroptera. A Key with Ecological Notes. FBA, Ambleside.

Rubber-necking the rare Rothschild Giraffe

The giraffe (Giraffa camelopardalis) is of course a familiar and unmistakeable animal - it is however much less common than often imagined. It is split into a number of subspecies (up to nine, depending where taxonomic boundaries are placed) and even the most common, the Maasai giraffe G. c. tippelskirchi numbers no more than around 40,000 individuals in the wild. Several subspecies number no more than a few hundred, one of which, the Rothschild giraffe G. c. rothschildi has an estimated wild population of less than 650 (all in protected areas of East Africa) with almost as many kept in zoos around the world (including Marwell's conservation programme where I took these photos, although I have seen them wild in the Lake Baringo area of Kenya - it is sometimes known as the Baringo giraffe). They are readily identifiable from the coat colour/pattern, especially the pale 'socks' due to a lack of pattern on the lower leg.

Rothschild giraffes at Marwell - a surreal sight in southern England!

Given the small population size, and ongoing threats such as habitat loss (e.g. encroachment by human settlements), widespread poaching, and possibly hybridisation, this subspecies was added as Endangered on the IUCN Red List in 2010. It is also a poorly understood subspecies with no major research being undertaken on it prior to the ongoing Rothschild's Giraffe Project which aims to look at the behaviour and ecology of wild populations, in particular, ecological/habitat requirements, group dynamics, factors affecting behaviour, social structure, herd formation and relatedness, and from all of this, knowledge about how to formulate effective conservation plans (if you'd like to donate to the project, you can do so here).


Like all giraffes, both sexes have short blunt horns called ossicones (formed from ossified cartilage and fused to the skull) - these contain blood vessels and may be involved in temperature regulation. Males compete by engaging in 'necking' behaviour - this starts by rubbing and pushing, and can develop into full-blown contests as males swing their heads at each other and try to land blows with the ossicones. If you ever get the chance to see this, it's amazing - like a huge game of conkers.

Their necks are of course their best-known feature - with just the usual seven cervical vertebrae, each is about 30cm long and they have ball-and-socket articulations for flexibility. Proportionally, newborn young have short necks with most of the elongation happens after birth, otherwise giving birth would be problematic. When upright, the neck is supported by the nuchal ligament and large muscles which create the small hump seen at the base above the shoulders. When bending down to drink or graze (which also means splaying or bending the legs), the network of veins and arteries called the 'rete mirabile', plus valves in the jugular veins, prevent excessive blood flow to the brain. These are just some of the circulatory adaptations that allow the giraffe to function with such as long neck - its heart rate (about 150 beats/minute) is high for a large animal, its heart weighs around 11kg or more generating blood pressure about twice that in humans, and the skin of the lower legs is thick and tight to prevent too much blood pooling there.

Rothschild giraffe bending down to graze - note the splayed front legs.

I could go on about the bizarre anatony of the giraffe, but I won't - instead, why not have a look at the excellent 'Inside Nature's Giants' TV programme (videos are on Youtube) based on dissections by specialists in their field. It's amazing I can assure you!

Focusing on the familiar V: dragonflies part I

A few months ago, a reader suggested I took an occasional look at some more familiar species. As my chosen remit is to popularise and familiarise less well-known species, I mused for a bit and then thought 'OK, why not?' which led to a short series on ladybirds. Now I have a garden pond, created and filled just a few weeks ago, and already interesting species are starting to appear, something I've been nattering about on facebook quite a bit. So, it seemed a good time to have a close look at one species in a generally popular group - the dragonflies - in particular the Common Darter Sympetrum striolatum. In Britain, this is probably the most commonly seen smallish red dragonfly (not to be confused with damselflies which are much more spindly), and is one of a number of species in a genus known in North America as 'meadowhawks'.

Male common darter Sympetrum striolatum on water mint.

First of all, its range is huge - from Ireland, Iberia and parts of North Africa eastwards through Europe as far as Japan, with migrations seen which can be huge in number. Like other Sympetrum, only mature males are red and it is these which I will focus on here. Females and immature males are yellowish as is typical for this genus.

The abdomen is almost parallel-sided (just a weak constriction in the front half) unlike others such as the ruddy darter S. sanguineum which has a more distinctively 'club-like' appearance. The abdomen is an orangey rather than deep red, while the sides of the thorax also have clearly yellowish patches (visible in the photo below).

Male common darter Sympetrum striolatum on Buddleia davidii.

As dragonflies can be variable in terms of depth of colour and other abdominal features, it is sometimes necessary to look more closely at the head to separate species in this genus. In S. striolatum, there is a black area above the 'face' running between the eyes, but this does not extend down the inside edge of the eyes (as shown in the photo below), unlike in, for example, S. sanguineum and S. vulgatum (which although common in continental Europe, is only found in southern Britain as a scarce vagrant).

Head of male common darter Sympetrum sanguineum showing limited extent of black facial mark.

So, if you are in Britain and see a red dragonfly of this shape and colour, there's a good chance it will be a male S. striolatum, but do take care as there are other options, and more so if you are on the continent. If you would like to find out more about this and other British and European dragonfly species, I've included a reading list at the bottom of this page - and if you'd like more info about creating a wildlife-friendly garden pond, why not download an advice booklet here (from the excellent Pond Conservation). Enjoy!

Male common darter Sympetrum striolatum surveying our new pond from his perch on water mint

Fascinating toxic frogs

I'm moving away from my usual topic today by looking at a species that is neither British nor invertebrate - the green and black poison arrow frog Dendrobates auratus. Poison arrow/dart frogs (they have several non-scientific names) are familiar to many people because of their toxicity and bright colours, but what is actually known about them?

Dendrobates auratus showing green and black colouration.

Well, first of all, although there are around 175 species of arrow/dart frogs (all in the family Dendrobatidae), only 3 are known to be used to coat blowpipe darts with poison, and none of these are in the genus Dendrobates. So, we know that the common name is not an accurate description - good start! Now onto a little background info.

Found in humid lowland and submontane forest and secondary vegetation up to about 1,200m altitude, D. auratus is native to Central America (Costa Rica, Nicaragua & Panama) and NW Colombia and, although many dendrobatids (like many amphibians worldwide) are rare and/or decreasing, this species is not currently threatened in the wild, being rated as of 'Least Concern' by the IUCN. There are also some feral populations in Oahu, Hawaii following a release of around 200 frogs in 1932 as an attempt to control non-native insects - these bred successfully and their descendents persist in the island's mountains and valleys (McKeown 1996). It is a highly variable species with at least 15 distinct colour forms known in the wild - as well as the typical green shown above, there is yellow, largely black, largely brown and the rare blue which is known from the Pacific side of Panama, but threatened with extinction due to clearance for agriculture, which fragments the habitat, though the species as a whole can live around humans (e.g. in parks, gardens and rubbish dumps (Heselhaus 1992, Ostrowski 2009). Being small (c. 20-40mm depending on form) and brightly coloured, tt is a popular pet among keepers of exotic herpetofauna and over-collection may be an issue, although there is a thriving captive breeding trade supplying much of the demand.

It is a semi-arboreal species, conducting much of its activity in trees up to some tens of metres above the ground but descending to the ground to travel between trees as it can not jump between them. Climbing is aided by pads at the ends of its toes (visible in the photo above). Females lay clutches of 3-13 eggs on leaf-litter which the male guards (Heselhaus 1992); they hatch after about two weeks and the male carries tadpoles to stagnant water in a tree-hole, leaf axil of a bromeliad, or small ground-level pool (van Wijngaarden 1990). The tadpoles feed on protozoans and rotifers, metamorphosing after 39-89 days, with sexual maturity being reached in 6-15 months, and a life-span of at least 6 years in captivity (Zimmermann & Zimmermann 1994). Females compete for males, attempting to monopolise them and being known to destroy the eggs of rivals (Summers 1989). If you would like to hear a brief recording of their call, go here.

Although not the most poisonous of dendrobatids, it is toxic enough to make a human unwell with skin glands producing an alkaloid derived from the ants that form much of the wild diet (Caldwell 1996). This reduces the risk of being attacked by predators such as theraphosid spiders AKA tarantulas (Gray et al. 2010), although some of the development of toxicity (e.g. in different popualtions, and captive-bred individuals fed a wild diet) are not fully understood.

So, to finish, why did I decide to look at this species? Well, it is a charismatic species and makes a change from my long run of invertebrate posts. I am also a member of Hampshire Conservation Volunteers - our logo is a frog so we adopted a D. auratus (now named 'Den Bates') at Marwell Wildlife and I wanted to know more about it - if you like this idea, the yellow and black D. leucomelas is still available for adoption...

Mate-guarding in Dendrobates auratus

References

Caldwell, J.P. (1996). The evolution of myrmecophagy and its correlates in poison frogs (Family Dendrobatidae). Journal of Zoology (London) 240(1): 75-101.
Gray, H.M., Kaiser, H. & Green, D.M. (2010). Does alkaloid sequestration protect the green poison frog,
Dendrobates auratus, from predator attacks? Salamandra 46(4): 235–238.
Heselhaus, R. (1992). Poison-arrow Frogs: Their Natural History and Care in Captivity. Blandford, London.
McKeown, S. (1996). A Field Guide to Reptiles and Amphibians in the Hawaiian Islands. Diamond Head Publishing, Los Osos, California.
Ostrowski, T. (2009). Dendrobates auratus.  [accessed 13/08/2012].
Summers, K. (1989). Sexual selection and intra-female competition in the green poison-dart frog, Dendrobates auratus. Animal Behaviour 37(5): 797-805.
van Wijngaarden, R. (1990). Enkele klimaatgegevens en waarnemingen in de biotoop van de gifkikkers Phyllobates vittatus en Dendrobates auratus. Lacerta 48(5): 147-154.
Zimmermann, E. & Zimmermann, H. 1994. Reproductive strategies, breeding, and conservation of tropical frogs: dart-poison frogs and Malagasy poison frogs. In: J.B. Murphy, K. Adler and J.T. Collins (eds). Captive Management and Conservation of Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, Ithaca (New York). Contributions to Herpetology Volume 11, pp. 255-266.

Dragon Hunt 2012

Nope, this is not about Harry Potter or video-gaming, so if that's what brought you here, sorry - but do feel free to stay and read on... instead, it's about Hampshire Conservation Volunteers' annual pilgrimage to see the dragonflies in one of the most Odonata-friendly parts of the New Forest.

This year's event which took place last Sunday was of particular interest as it follows an exceptionally wet early to mid-summer in Britain which has led to dire predictions about the fate of many invertebrate species, a topic I've looked at briefly here. Of course, the Odonata (damselflies, demoiselles and dragonflies - all of which are illustrated below) are aquatic as juveniles, and require water to breed as adults, so it is less clear what effect wet conditions might have than, for example, on butterflies. However, with heavy rains come lower-than-average temperatures, so some of the same impacts might be seen in the adults, such as difficulties finding food and mates.

For those not familiar with Odonata, the damselflies and demoiselles (suborder Zygoptera) are slender-bodied and hold their wings closed lengthways at rest, while the dragonflies (infraorder Anisoptera) are more robust 'typical' Odonata and hold their wings open at rest. There is another infraorder of dragonflies, the Epiophlebioptera, but most of these are extinct with just three Asian species currently known (the third was discovered recently in China by Li et al., 2012) - I won't worry about these here, so back to the Dragon Hunt...

Our first stop was Hatchet Pond, a well-known Odonata-watching spot where it is possible to track down some botanical rarities too (more on that another time) and which provided us with good views of familiar species such as Common blue damselfly (with various female colour forms, and both pale-immature and blue-mature males, plus egg-laying behaviour seen) and an Emperor dragonfly patrolling a section of the large pond (it's the largest in the New Forest). However, although we visited a couple of the small nearby ponds as well, the best views of the day - and the most interesting records - were around the nearby stream at Crockford, where one of the first things we noticed (and we were helped by the sunnier-than-forecast conditions) was a number of very active Beautiful demoiselles, including males trying to entice females with a fluttering wing display.

A male (note the claspers at the tip of the abdomen) Beautiful demoiselle Calopteryx virgo.

We also couldn't help but notice a much larger species flying rapidly back and forth along a section of stream, the typical male territorial behaviour of the Golden-ringed dragonfly. The length of stream patrolled depends on the density of males present as they turn back to fly the other way when another male is encountered. Although territories are generally not guarded very vigorously, aggressive encounters between males will sometimes occur when they meet - there were 3 males along this stretch and they did encounter each other more than once. They are especially active during this period of territorial behaviour and hence can be difficult to photograph, but as they occasionally pause on vegetation, patience is generally rewarded.

Golden-ringed dragonfly Cordulegaster boltonii hanging from a twig.

Of the 14 species recorded (the list, including scientific names, is below), one is a rarity in Britain, associated largely with central southern England (though it is widespread in continental Europe), and that is the Southern damselfly. It is found mainly in slow-flowing base-rich ditches and streams in acid heathlands (and also in some of Hampshire's chalk streams, one of which is about 500m from where I live despite being urban-based, lucky me!), and seems to be limited by needing water which is stable in temperature, rarely dropping below 10^oC, clearly a potential limitation during winter. However, at Crockford, numerous individuals were seen, including (again, a little patience was required) some that would tolerate a human presence near enough to see the 'mercury' mark that distinguishes it from other blue damselfly species.

Southern damselfly Coenagrion mercuriale showing the identifying 'mercury' mark near the front of the abdomen.

More importantly, active breeding behaviour could be seen - I have witnessed this before in the Southern damselfly, but never in quite such large numbers. The photograph below shows three pairs at different stages of mating. On the left, a pair which is unattached (and may simply be resting on vegetation), on the right, a male has gripped a paler female with his claspers, and at the top, the typical 'mating wheel' arrangement seen during copulation. It's not often an opportunity for a shot like this comes around...

Three pairs of Southern damselfly Coenagrion mercuriale

Of course, it's easy to get a little spoiled and forget that despite the numbers seen during the Dragon Hunt, this is actually a rare species in Britain and is covered by a UK Biodiversity Action Plan as well as being listed in Schedule 5 of the Wildlife & Countryside Act 1991 which prohibits handling without a licence.

Looking at the day's records as a whole, what does it say about the Odonata community in the area we visited? Well, it's only a snapshot, but a fair number of species were seen even though a few that I expected to see were not noted (this doesn't mean they weren't there of course) such as Emerald damselfly (Lestes sponsa) and Red-eyed damselfly (Erythromma najas). On the whole, the blue damselfly species were reasonably abundant along with the darters and skimmers (Libellulidae), but the red damselflies were sparse, as were the large hawker dragonflies (Aeshnidae) with just two Emperor dragonflies and a single Migrant hawker seen. Is this a real effect of poor weather? Well, without a more systematic study, it is of course impossible to tell for certain, but as Corbet & Brooks (2008) note using various examples (and noting the need for targeted study), Odonata are temperature-limited, so it seems likely that some impact might occur. However, volunteer records such as those here can only help to build up a picture of the current status of Britain's Odonata populations.

The day's Dragon List

Azure damselfly (Coenagrion puella)
Beautiful demoiselle (Calopteryx virgo)
Black-tailed skimmer (Orthetrum cancellatum)
Blue-tailed damselfly (Ischnura elegans)
Common blue damselfly (Enallagma cyathigerum)
Common darter (Sympetrum striolatum)
Emperor dragonfly (Anax imperator)
Golden-ringed dragonfly (Cordulegaster boltonii)
Keeled skimmer (Orthetrum coerulescens)
Large red damselfly (Pyrrhosoma nymphula)
Migrant hawker (Aeshna mixta)
Ruddy darter (Sympetrum sanguineum)
Small red damselfly (Ceriagrion tenellum)
Southern damselfly (Coenagrion mercuriale)

More about dragonflies...

If you are interested in identifying the Odonata of Britain and Europe, the following books are all excellent (there are others, but these are my personal favourites):

Brooks, S. (2004). Field Guide to the Dragonflies and Damselflies of Great Britain and Ireland (revised edition). British Wildlife Publishing, Gillingham.
Cham, S. (2007). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 1: Dragonflies (Anisoptera). British Dragonfly Society, Peterborough.
Cham, S. (2009). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 2: Damselflies (Zygoptera). British Dragonfly Society, Peterborough.
Dijkstra, K.D. (2006). Field Guide to the Dragonflies of Britain and Europe. British Wildlife Publishing, Gillingham.
Smallshire, D. & Swash, A. (2004). Britain's Dragonflies. WildGuides, Old Basing.

...and the New Forest

Brock, P.D. (2011). A Photographic Guide to Insects of the New Forest and Surrounding Area. Pisces, Newbury.
Tubbs, C.R.. (2001). The New Forest: History, Ecology & Conservation. (2nd ed.). New Forest Ninth Centenary Trust, Lyndhurst.

References

Corbet, P. & Brooks, S. (2008). Dragonflies. HarperCollins, London.
Li, J.-K., Nel, A., Zhang, X.-P., Fleck, G., Gao, M.-X., Lin, L. & Zhou, J. (2012). A third species of the relict family Epiophlebiidae discovered in China (Odonata: Epiproctophora). Systematic Entomology 37(2): 408-412.