Twin Spotted Sphinx Info
Hi! I recently came upon a mortally wounded female of this variety, and brought her home to care for her (hopihg she would be able to fly again by the time I got her home so i could release her). She began laying eggs up until she died a few days ago, and I carefully transplanted the eggs to a ventilated jar, so they could hatch and I could care for them. I was wondering how big they'll get, what the ideal food for them is, and how long it will take before they chrysalis. Thanks! -Josh
Worcester County Massachusetts
Hi Josh----I am located about 2/3 of the way across the country from you, so I wonder sometimes how I get assigned these questions? Anyway---looking at the book, Caterpillars of Eastern North America by David Wagner, I see a couple of possible IDs for your moth since he included photos of these particular adults. Twin-spotted sphinx is Smerinthus jamaicensis, p 261, and blinded sphinx, Paonias excaecatus, p. 262. Both have brown tone patterns on the forewings, pink on the hind wings and dark eyespots. There are definitely 2 spots/wing in his picture of the twin-spotted sphinx. On your photo, I can't quite see if the spots are divided or not in each eyespot. Looking at the patterns on the forewings and especially that marking on the thorax (sort of rocket-like) on the Paonias, I'm leaning a little more toward that genus for the ID. Also, he notes that this Paonias is the 'most commonly encountered sphingid in many Northeastern hardwood forests.' If you go to the website called bugguide you can type in these names and compare photos of each to your specimen.
Wagner lists common food plants for the larvae of each of these. You may have easy access to some of these trees in your area: aspen, poplar and willow were listed for the twin-spotted; poplar and willow were listed for the Paonias, along with American hornbeam, apple, basswood, beech, bird, cherry, chestnut, elm, hawthorn, hop hornbeam, oak, rose, serviceberry, spirea, and 'undoubtedly many other woody plants. It appears poplar and willow could keep the caterpillars happy and well fed whichever species it actually is---good news.
I don't know how long the eggs would develop before hatching, assuming the female mated earlier. However, tomato hornworm---another sphingid---can hatch in about a week. Their caterpillars develop over 3-4 weeks before pupating. Insofar that large caterpillars could easily reach the length and girth of your index finger---or more---that could mean a lot of leaf collecting and cage cleaning. If you're going to go that route, you might want to think about an empty fish tank as a cage and maybe clipping some host twigs with several leaves. Make a small 'bouquet' of twigs and put the cut ends into a narrow-mouth bottle or jaw with water. Use several of these in the tank, replacing twigs and foliage as needed.
Depending on how many caterpillars hatch, you could be busy. Keep the cage as clean as you can to decrease the likelihood of various microbes getting a foothold and killing your caterpillars. Caterpillars can be difficult to raise in artificial circumstances, but it can be a fun project. Good luck.