Parasite Flies

My trip to Kentle Wood on Tuesday, 16 July, resulted in no sensational finds but I was quite pleased to record two 'Parasite Flies'.


The is a name frequently applied to members of the Tachinidae family - and it is well deserved. It is a huge family (the second largest family of diptera) with something like 8,300 species known across the world and about 245 species found in Britain.


Superficially they are rather ordinary-looking flies and to the non-entomologist could easily be passed over as some sort of house-fly or blow fly, particularly as the most significant identification feature, a prominent subscutellum, is not at all obvious.

So, as I say, these flies are parasites and, using various strategies, manage to introduce their eggs or larvae into an unfortunate host, which is then eaten away. Occasionally the host survives but usually the attack is a death sentence.

We may find this horrifying but outside of the tachinids many insects behave as parasites including the Chigoe Flea or Jigger, Tunga penetrans, the fertilized female of which burrows into the skin of several mammals including humans. In the case of humans the feet are generally affected.

Attacks by Chigoe Fleas can have very unpleasant consequences but are

not fatal.

Death does not result, so the Chigoe Flea is a parasite, whereas creatures where the parasitic attack leads to the death of the host are parasitoids

In Britain a rather common blow fly, Lucilia bufonivora, lays its eggs on toads (and occasionally frogs), with unpleasant consequences. The larvae invade the host, usually via the nostrils and their attack generally leads to its death.(bufo = toad; vorare = to devour)

Lucilia bufonivora is quite common and I have taken specimens in

the Daventry area.

As far as tachinid flies are concerned a range of insects may be attacked including sawflies, beetles, earwigs and centipedes, but as far as I am aware vertebrates are not invaded. If, as I say, they look like 'ordinary' flies, how are they recognised? I use two clues. One is the posture the flies adopt when at rest. Their wings are swept back in a rather distinctive V shape. The other feature is a bristly-hairy appearance.

Linnaemya picta was present in Kentle Wood on 16 June, 2020

The first tachinid I recorded in Kentle Wood was Linnaemya picta, and the picture displays the bristly nature of the abdomen. The presence of this fly in Britain was not recognised in Britain until 2009 (although it may have been present long before that). Since then I have found it in a number of locations but this was a 'first' for Kentle Wood. In general it is a fairly typical tachinid fly.


The other species taken was Dufouria chalybeata* and is slightly less typical in that the body is a uniform glossy black, unlike the 'mottled' appearance of Linnaemya. It was also new to Kentle Wood.




Dufouria chalybeata has a glossy black appearance and its bristly nature
is clear in the picture

The flies required microscopic examination for in both cases the precise identification depended upon the position and number of tiny bristles. Great fun! Incidentally Dufouria and Linnaemya are parasites of leaf beetles and noctuid moths respectively.

All the pictures have been lifted from the internet and I have been unable to find the name of the photographers concerned. Apologies and thanks.

* The use of 'chalybeata' as a specific name was, I confess, a slight puzzle. It turns out to mean steel-blue. Chalybeate water contains iron compounds (a number of villages around Northamptonshire boasted chalybeate springs and they also led to the fame of, for example, Tunbridge Wells as a spa) and the name originated with the Chalybes, a group of people living in Turkey in ancient times, famous for their skills in iron-working.