Tachinid flies (Tachinidae) are a prime example of the many
beneficial, but mostly unseen, creatures that make it
possible for us to enjoy naturally healthy gardens without
the use of pesticides. They are small and inconspicuous,
but they are doing a mighty big job for us.
Tachinids parasitize other insects. They employ a variety
of tactics as “the party guest from hell” when
they move in, uninvited, and proceed to eat their hosts.
They may glue their eggs to their host or lay their eggs on
foliage where the host larvae will eat them. Some have
ovipositors with which they inject their eggs directly into
the unsuspecting host’s body.
Extremely beneficial because of their diversity, tachinids
also can be very under-appreciated due to their small size
and unseen activities. They help control garden pests such
as gypsy moths, cabbage loopers, Japanese beetles,
armyworms, cutworms, sawflies, codling moths, peach twig
borers, pink bollworms, tent caterpillars, squash bugs and
The scientific information is rather general concerning
tachinids. Only a few of the 1,300 North American species
have common names, and only about 20 percent can be
identified with a hand lens and field guide.
Tachinid flies are similar in shape and size to houseflies
(usually less than a half inch in length) but they usually
project a few stiff hairs backwards, over and slightly
beyond the abdomen. Most of them are considered rather drab
The tachinid species that seek out moth and butterfly hosts
usually glue their eggs to the moth or butterfly larvae;
after the eggs hatch, the resulting fly larvae bore into
their host, eventually killing it. When beetles are the
host, either larva or adults can be parasitized, depending
on what kind of tachinid is involved. Tachinids usually
attack adults of the true bug and grasshopper orders.
Egg and larvae development happen quickly in tachinid
flies. Many species pass from the early stages to adulthood
in just three to four weeks. If the host also moves through
life stages quickly, several generations can be produced in
one garden season.
After a larva has invaded or formed inside the host, it
maintains respiration by either attaching its breathing
(posterior) end to its victim’s tracheal system or
leaving that end protruding from the victim’s body.
Research is ongoing on several species of tachinids; to
date, the cutworm type has been shown to reduce populations
of the variegated cutworm, the army worm and the
yellow-striped army worm.
Unfortunately, tachinids are not available as commercial
pest controls, but the adult flies feed on nectar, so you
can attract them to your garden by growing plants with
umbel-type flowers, including carrots, cilantro, dill,
coriander, buckwheat and sweet clover. — John Stuart
(For more about beneficial insects, see “ Protect
Your Garden with Beneficial Bugs ,” Page 74.)