Species of the week- 7

Sorry this blog is one day late! I suffered from Cornish internet problems when I intended to write this last night. The species this week is from an underappreciated family of Insects: Formicidae, otherwise known as Ants. There are around 50 species of Ant that can be found outdoors in Britain, and this species is amongst the least conspicuous of them all. It is (of course) Stenamma debile! Unfortunately, there is no common name for this species. Here it is:


It isn’t the clearest phone-microscoped picture I’ve ever taken, but the ant is only about 3mm long! I admit, that compared to some of my previous ‘species of the weeks’, S.debile isn’t exactly stunning, but I hope I can persuade you that it’s still fascinating!

I chose S.debile this week, as myself and a friend Jaimie found two individuals whilst sifting leaf litter around College Reservoir (which, by the way, has a stunning juvenile Pectoral Sandpiper wading its shores at the moment!). This was the first time that I’d seen S.debile for three and a half years! The reason I see this species so infrequently isn’t that it’s especially rare, just that it’s extremely hard to find. It makes very small colonies (usually only 20-50 workers), which live in the soil under leaf litter, so the chance of stumbling across a colony is remote. If (by chance or dedication) you do manage to pick up a sample of leaf litter containing S.debile, your struggles aren’t over! This species is soil/leaf-coloured, 3mm long, moves very slowly, and tends to roll into a ball when disturbed!

Luckily, identifying S.debile when you find it is quite straightforward. General size and shape is usually a good indication, but the features to look for are: 

1) It has two waists, the first of which is relatively longer and thinner than in other ant genera.

2) It has very tiny eyes compared with most other ant genera.

3) It has only very short spines at the back of the thorax (overhanging waists). These spines are longer and thinner in most other ant genera.

4) The long, thin first waist has bulging nodes on each side near its joint to the thorax. This features separates S.debile from the much rarer S.westwoodii, which has no such nodes.

These features can all be seen fairly well in my photo below.


Workers of this ant species are probably mostly scavengers of small dead  invertebrates, but it is likely that they will take live prey if it is small, and slow enough for them! S.debile is a fairly widespread (but as outlined above, probably hugely under-recorded) species, but seems to be quite thermophilic, not having been recorded any further North than Lancashire yet. It has had very few records from Cornwall so far, so I’m very pleased to have found it! Here’s its distribution map:


I wish anybody who tries to find it the best of luck!


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