Thomisidae: Crab spiders

This family is closely related to the running crab spiders Philodromidae. There are 26 British species. They are broad-bodied, with the front two pair of legs are much longer and stouter that the others and furnished with stout spines, which they often hold wide open in a manner similar to the way a crab hold its front legs open defensively. This, together with their widely spaced eyes placed on tubercles and their ability to walk sideways has given them their common name. There can be substantial colour and size polymorphism, with smaller and more cryptically coloured males.

Ambush predators on flowers
Crab spiders do not build a hunting web. Many species of crab spiders use a sit-and-wait strategy to hunt insects. They sit on a flower immobile, front legs open and rear legs holding them to the substrate, relying on their cryptic colours to avoid being seen by visiting pollinating insects (top shot shows Misumena vatia. Credit: Alan Shearman, CC BY-NC-SA 2.0). As soon as an insect lands on the flower the spider will swiftly bite it catch it. Other species can also stalk prey, cat style, while on the ground, or low vegetation. More on a BugBlog post here.

Xysticus cristatus stalking a fly.

Xysticus cristatus on dandelion, using the sit-and-wait strategy.

Colour changes
Crab spiders are very diverse in shape and colour and some species are very colourful, but yet, remarkably camouflaged in their habitats. Some species, such as Misumena vatia are able to slowly change colour to match the flower where they are sitting. Adults can change colour from yellow to white or greenish with or without pink lateral markings, and most of the time it matches the colour of the flower it is sitting on.

Female Xysticus cristatus

Male Xysticus cristatus

Common Darters

There were at least two male Common Darters, Sympetrum striolatum, around the wildlife garden pond today. If you move slowly, they are great posers and allow very close approximation. Their faces are locked into a perpetual smiling grimace, adding to their charm. If you watch them from a close distance,  you'll notice that they are constantly flicking their heads around, looking for insects flying overhead. If a suitable one is detected, they dart off, returning to their perch to eat their prey.

The ever smiling darter

A short clip of the darter watching for prey.

Crab spider stalking fly

I spotted this crab spider in my local wildlife garden, it had this strange clock-work movement and grabbed my attention. Then I spotted the fly. The crab spider, a female Xysticus cristatus, legs outstretched, on the left of the photo. The large fly is on the right, having fed or drank from the base of a teasel leaf. If you want to know what happened next see this video.

The hoverfly nightmare

Yesterday morning I found this Ectemnius wasp on a plant pot. Usually, they are very active and are flighty, but this one was still cold and let me take some close ups. Ectemnius are digger wasps that hunt flies - including hoverflies - for their larvae to feed. They dig a tunnel in wood and stock cells with flies, laying their eggs in them. They are several similar species, that can only be distinguished under the microscope. The microscope, however, is not needed to appreciate two of the weapons that these wasps use for hunting: their amazing, large, envolving eyes - note the antennae nicely folded between them, not occluding their field of vision, and their fearsome jaws, folded under their head.