Chrysotoxum cautum

Date First Recorded in the Garden: 31/05/2021

Family Syrphidae: Hoverflies

A very familiar and attractive family of flies belonging to the insect order Diptera (or True Flies). They have a single pair of wings, unlike most insect orders that have two pairs. Many species of hoverflies sport a yellow/black colour combination and are therefore often mistaken for bees or wasps, which many hoverflies attempt to mimic. However, they lack the ability to sting and are totally harmless.

With over 280 species recorded in the British Isles, most gardens will at some point in the year play host to more than one species. Many species are considered beneficial as their larvae feed throughout their development on aphids.

Interestingly, in most hoverfly species sex can be determined simply by looking at the hoverflies eyes. Usually if the eyes meet at the top of the head, then it’s a male; if separated then it’s a female. There area few species where this doesn’t hold true because they have males with eyes that are separated, however if they do meet you can be sure its a male.

Chrysotoxum cautum

According to Britain’s Hoverflies – A Field Guide (*1), there are eight species belonging to the genus Chrysotoxum recorded in Great Britain. Whilst we are reasonably confident that we have identified the species above correctly as C. cautum, we have to acknowledge it could be one of five possible species. Three of the eight British representatives, such as the species Chrysotoxum festivum, can be easily discounted based on the characteristic yellow abdominal markings not extending to the edge of the abdomen, as noted on our C. festivum species account found HERE.

The remaining five species are difficult to tell apart. However, we can make some informed assumptions. One of the five is Endangered, whilst another is Nationally Scarce. The remaining 3 species are all common, but C. cautum is the most frequent in our area. The Field Guide (*1) also provides other hints based on appearance which in general support our identification as C. cautum (see antennal note below).

Another characteristic of this species is that the first 2 antennal segments are approximately the same length when combined as the third segment, as shown below.

Various sources state the larvae feed on root aphids, but it seems no one actually knows for sure.

*1: Ball, S & Morris, R. (2015)Britain’s Hoverflies A field guide. Oxfordshire: Princeton University Press.