Subject: Re: Can pupae 'dig' is the question

From: "A.P.K.Torry" <[email-masked]>
Date: Fri, 10 May 1996 09:20:22 GMT

James Kruse asked about pupae and their ability to 'dig themselves out of a
hole'

>    This brings me to a question.  With Sphingids or Saturniids which
>the larvae pupates under ground...  How does the pupa, about to molt
>to adult, with the exoskeleton thinned and soft get out of the
>hard field soil and sod layer?  When you are rearing them in peat moss
>and potting soil its not a big deal.  This was a question when I was
>a kid and I still have yet to hear the explaination.  Surely the
>adult doesn't do it, no digging apparatus.  The pupae of which I
>speak have the gin-traps on the sides and spike on the tip of the
>abdomen...  I have noticed that the pupae I unearth before spring
>seem to know that they are out of the ground, as they burst from
>their pupae without so much as a twitch of the abdomen.
>
I few years ago I reared some Privet Hawk moths (Sphinx ligustri) which bury
themselves a good foot into the soil before pupating, to prevent
interference by other larvae I placed 1 caterpillar each into 400g coffee
jars filled with soil (Not peat or compost but good old fashioned dirt),
about half of these larvae pupated at or very close to the bottom of the
jars and formed there pupal 'chamber' actually touching the side of the
glass jar thus allowing me to see the larvae pupating.

In the spring, just before emergence (end of May) I made a specific effort
to monitor theses pupae as they emerged and I can saw the adult emerge from
the pupal case and start digging it's way upward it seemed to find the going
very easy and I conjectured that it was returning to the surface via the
original tunnel which the caterpillar had made the following autumn, if this
was the case then the adult is either scenting something left by the
caterpillar or is sensing the looser soil, whichever it is the adult used
it's very strong forelegs to 'scratch' at the soil.

Hope this helps a little.

Andrew