Ant-mimicking spider (Micaria sp) Photo by Phil from https://www.flickr.com/photos/57984606@N00/5634004157/

Dear Readers, after our spider walk a few months ago, the walk leader, Edward Milner, was investigating some dead wood on a tree opposite Coldfall Wood in East Finchley when he found a small spider. Uncertain of what it was, he took it home and was able to identify it as a species of ant-mimicking spider that had only been found once in London before – Micaria subopaca.

Ant-mimicking spiders look very like ants, as you can see from the photos above, and can often be found running around ‘in a manic, ant-like fashion’ according to my Collins Field Guide to Spiders. Sometimes they associate directly with the insects – as far as we know, the spiders don’t actually eat ants, but it may be that they look enough like them to deter predators (many ants are aggressive and will bite or spray formic acid as a defence). The spiders have iridescent abdomens that are said to gleam in bright sunshine. They hunt during the day, and although little can move extremely fast.

Micaria subopaca can usually be found running about on tree bark – it’s particularly fond of pine trees. The spider that Edward found wasn’t on a pine tree (he thinks it was could have been a rowan) but sadly we shall never know, as the tree has been cut down and now there’s just a stump. It’s easy to forget how many tiny creatures might depend on a single tree, and this is a particularly sad case, owing to the rarity of the spider. This species loves trees in warm, dry positions, so let’s hope that it’s transferred to a nearby tree with a similar microhabitat. Edward hasn’t given up hope of finding another one of these spiders, maybe in Coldfall Wood itself, and if anyone can find one, he can, so fingers crossed.

Footnote: the different species of ant-mimicking spider look extremely similar, so it’s sometimes only possible to identify to species level using a microscope, which is how this spider was identified.  In this case there are two other species (M.pulicara and M. micans) which are much commoner, but look almost identical. It’s one reason why having people who are experts in taxonomy is so important – if we don’t know what species are about, how can we even hope to protect them?