The (not really) attack of the (not actually) killer spiders!

Over the last few weeks, there has been a flurry of lurid headlines about 'killer spiders' and bites leading to horrible consequences, for example this one which was actually due to a streptococcal infection rather than spider venom - and of course infections can get into any skin puncture, but the tabloid fervour doesn't bother to mention this. In reality the spiders are the false widow Steatoda nobilis which bites few people - the species is not aggressive and there are no confirmed reports of anyone being hospitalised due to the venom. There can be bite symptoms such as chest pains and tingling in the fingers but nothing like the horror-stories in some sections of the media. Sadly, the media frenzy has led to people squashing them on sight and even closing a school where they were found - a major over-reaction in my opinion due to ill-informed health & safety officials being influenced by stories of poisoning and 'infestations'. Yes, it may be Britain's most venomous spider, but there really isn't much competition for that accolade - we have nothing like the Sydney funnel-web here. As it happens, I have one living in my garden storage box, and she's really quite pretty and although she tends her spiderlings carefully is quite timid and curls up behind her web if I point the camera too close. She does not leap at me, fangs clashing and venom dripping. Then again, a headline like 'mostly harmless spider occasionally causes minor irritation' wouldn't sell many papers...

Steatoda nobilis with spiderlings in our garden storage box

Fortunately there are more reasoned sources of information such as the Natural History Museum who get a lot of calls about this spider, and some rather better reporting about why they aren't anything to be scared of after all such as here and here. Yes, they are spreading (probably due to climate change) but have been in Britain since the 19th century and have been expanding their range significantly for 15-20 years - the 'outbreak' over the last few weeks is clearly more to do with awareness with more people noticing them (and panicking) following the 'killer spider' headlines. Still, it was interesting to get an unexpected call from the Guardian yesterday wanting to interview me about the spider - I was happy to do so, and the resulting article is here. The invertebrate conservation charity Buglife has an excellent page about spider bites, including advice about what to do in the unlikely event you are bitten and develop symptoms. So, happy spidering, please don't squash them, or have nightmares about them - they'll eat plenty of your garden and household pests if you let them.

The ladybird and the cocoon of doom

About 10 days ago, while cleaning one of my stick-insect cages, I noticed an adult 7-spot ladybird Coccinella 7-punctata with a silky cocoon stuck between its legs. Ladybirds don't make cocoons like that - what could it be? Some small invertebrates can be truly difficult to identify, but this one was, for once, straightforward as it is a common parasite of several ladybird species, Perilitus coccinellae, a wasp in the family Braconidae. But, to be sure I put the cocoon in a hatchery and waited...

Perilitus coccinellae cocoon, approx 6mm long

An adult P. coccinellae (a female - males are unknown) did indeed emerge and provides a good opportunity to look at a common, but often overlooked parasite.

 

Adult P. coccinellae - note the wing venation and the needle-like ovipositor with the abdomen curled under the body

Adult P. coccinellae - a closer look at the ovipositor

Adult P. coccinellae - see how the abdomen is curled under the body

The wasp has an interesting life history (as parasites often do). Although ladybird pupae are sometimes targeted, adults are usually parasitised. The wasp taps the ladybird with her antennae then curls the ovipositor forward and begins to tap and probe for weak points, laying a single egg into the ladybird along with trophic ('nutritional') cells which absorb food from the host so the wasp larva can feed on them once it hatches. It does not feed on the ladybird directly, although the diversion of nutrients to the parasite ipacts on the host's reproductive development and fat storage. After reaching its 4th instar, the larva chews its way out from the underside of the ladybird's abdomen, having immobilised it, possibly by affecting the host's motor neurones. It then forms the cocoon which is attached to the ladybird's legs. The ladybird is alive at this point which means that the wasp is protected by its warning colouration and reflex bleeding defence. The wasp then pupates, emerges as an adult and seeks a new host as soon as its wings are dry. The ladybird usually dies within about a week, either of starvation or fungal disease. Some host ladybirds do regain the use of their limbs although most are greatly weakened and die soon after. In winter the cycle stops for a while as the wasp larva hibernates within a host ladybird.

So, a bad end for the ladybird, but an interesting tale - if you'd like to read it in more detail, try Majerus (1994) which contains plenty more interesting ladybird info.

Reference

Majerus, M.E.N. (1994). Ladybirds. HarperCollins, London. [New Naturalist series]

The first fog of autumn

A non-technical post today - I'm mired in a swamp of academic marking, so something soothing is required... fortunately I woke up to a foggy morning which highlighted just how busy the spiders in our garden have been - enjoy!

A fine orb-web made by the garden orb spider Araneus diadematus

A large female garden orb spider Araneus diadematus at the hub of her web

A web shaped as a platform suspended from twigs and leaves - it reminds me of a mountaineering tent attached to cliff with pitons. Possibly made by a Theridion species, and there may be webs of spiders such as Linyphia tangled into it.

An incautious wasp becomes a meal for Araneus diadematus