QUODDY NATURE NOTES – Tachinid Flies

Tachinid Flies

Red-butted tachinid

A scraggily red-butted tachinid fly, probably Hystricia abrupta

Nature is a pretty wondrous system, but not all of the time what we as people would consider nice, whatever the definition of ‘nice’ is.  As we learn more about the different organisms, most actions that they exhibit are sort of understandable, but this gets pretty dismal in the insect class, and any sense of decency and fair play really goes to hell in a hand basket when we look into the grisly life style of Tachinid flies.  Not that it’s bad; there is no such thing as ‘good’ or ‘bad’ in nature, it just might be a lot different than what we expect.

Tachinid flies are in the order Diptera, or true flies, that is, they only have two wings.  Worldwide there are probably over 15,000 species of Tachinid flies, and here in North America we have over 1300 species.  All tachinid flies are parasitoid in their larval stage and their unfortunate hosts are almost exclusively insects.  A parasite is a freeloader on a host, but a parasitoid is a species that as a larva kill their host before proceeding on to their adult stage.

The overall effect of tachinid flies is enormous and not fully understood, and not always beneficial.  Tachinid flies come in many different shapes and colors and range in size from an eighth of an inch to a giant three-quarters of an inch long.  They are pretty well represented on all land masses except Antarctica, and more common in the tropics, but not very common on offshore islands.

I’m not sure how many types of tachinid flies we have here in Maine, or if there are more or less of the critters nowadays, but I think I just might be more aware of them.  Looking for butterflies, one cannot help seeing the fat, scraggily but innocent looking fly with the bristly, reddish butt sucking up nectar.  This guy is probably Hystricia abrupta, and it has no common name, and the Missus is known to parasitize tiger moths caterpillars, like the Woolly Bear.  I don’t know if H. abrupta attacks other fuzzy caterpillars, like the infestation of the black and white Hickory Tussock moths we had last year , but we certainly have fewer of these caterpillars this year.

Generally, each tachinid type will use its own method to parasitize the host.  They may attach their eggs or larva to the host or lay their eggs or larva on the plant and the host may eat the eggs and get parasitized or the larva may attach itself to the host or the fly may inject their eggs directly into the host.  In all cases the larvae eventually consume and kill the host.

If the host has many larvae and is not of sufficient size, the larvae will consume each other until only a few survivors remain.  Besides caterpillars, tachinids parasitize many types of grasshoppers and beetles, the most famous of the latter being the Japanese beetle.  If you see a Japanese beetle with little white bumps on it, let it be and don’t throw it into your soapy water bucket.  In a few weeks you will have more tachinid flies Hypererecteina aldrichi.

Tachinid flies are generally beneficial in the long run, but introduction of biological controls can be complicated.  Will the tachinid just attack the target species and faithfully disappear after its job is done?  A tachinid fly introduced many years ago to combat the infamous Gypsy moth has been implicated in the decline of giant silkworm moths (Saturniidae) in New England.  The caterpillars of the Monarch butterflies are known to be attacked by tachinid flies of genus Archytas.

There seems to be very few Monarchs this year.  Let me know if you see any, and when and where.

Tachinid fly

A typical tachinid fly