Tachinid Fly Infestation of Monarch Caterpillars

I seem to have a bad case of tachinid fly infestation of my current batch of caterpillars. I sometimes put final instar caterpillars into a jar since they often get eaten by the paper wasps around here and it seems like such a waste that they have eaten all those precious milkweed leaves, only to serve as wasp buffet.

Normally with tachinid fly the larvae don't emerge until the caterpillar has pupated, but recently I noticed a caterpillar had died on the bottom of the jar. When I took a closer look I noticed there were EIGHT tachinid fly larvae on the bottom of the jar! That has to be an all time record! Normally I see just one or two.

Signs that monarch caterpillars are infested with tachinid fly larvae include caterpillars in their final instars that are lethargic, and pre-pupal caterpillars that hang limply instead of in the "J position".

Check out the photos below. See my previous post for more information on tachinid flies.

Monarch caterpillar that hosted 8 tachinid fly larvae. The larvae are the red
"sprinkles". The eighth one is peeping out from the leaves.
The black "sprinkles" are friss (caterpillar poop).

Pre-pupa monarch caterpillar hanging limply indicates infection with
tachinid fly larvae. This caterpillar will die before forming a chrysalis
and the larvae will descend from mucous-like threads in the next
day or so.