How we are Rearing our Monarchs

Our Monarchs (Danaus plexippus) have begun to hatch and in this post we briefly go over how we are rearing them in lieu of a full set of rearing notes since we have reared this species so many times.

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The 18 Monarch eggs (Danaus plexippus) we collected on 6/24 started to hatch yesterday and now we have a total of seven little newborns. Despite it being such a popular species, especially among beginners, most people who have reared Monarchs probably know that this species is quite prone to diseases and is often infected by the protozoan parasite, Ophryocystis elektroscirrha (OE), as well as tachinid flies (family Tachinidae). In the past, we have had some serious issues with both OE and tachinid flies in wild-caught caterpillars. This time, however, we have found the Monarchs in the form of egg, a rare find in the summer months here, so pretty much the only thing that they could potentially be infected with is OE (transmitted by their mother butterfly onto their eggs shells while are ingested along with the spores upon hatching) which is extremely common among our western populations. 

Sometimes we have used standard sterilizing protocols to get rid of the stuff, but it is a lot of work. Since we are currently dealing with a myriad of rearing projects right now, we just didn't have the time or energy to perform any sterilization procedures and are just raising them without special treatment. 

Anyway, we have set up a pretty simple rearing apparatus for our newborns since there are so few of them and they are still young and won't eat much. Basically, we used a small rectangular scientific flask filled with water to hold cuttings of Tropical Milkweed (Asclepias curassaciva). The milkweed is a pretty hardy plant and can easily be grown and transplanted from cuttings, hence the fact that the cuttings generally do well when simply placed in some water. We thought that this was the best and most natural alternative to rearing them outside since we do not currently have any proper outdoor rearing sleeves. 

On a completely different note, we took note of something we have noted for a while with Brush-foots (Nymphalidae) like Monarchs, West Coast Ladies (Vanessa annabella), and Gulf Fritillaries (Augraulis vanillae): the caterpillars are mildly cannibalistic of other eggs. From the 18 eggs, we were only able to get seven of them to hatch and the other eggs have seemed to have dissapeared into thin air. Because we did not remove the newborn caterpillars immediately after they hatched, they must have had the chance to walk around and eat up some of the other eggs that hadn't hatched yet (though we could be wrong). As for the evolutionary benefit, this is normally to avoid overcrowding, but to be honest it just seems illogical in many cases. 

- Brian