At the beginning of the month I was on our patio getting ready to have dinner when a black wasp fluttered heavily past me carrying a bright green load that may have outweighed it by a little bit. The wasp I recognized as a mason wasp, and the load it carried was the caterpillar larva of a small moth species. Hunting wasps are not generalists. They do not consume the insects they catch themselves, but rather provide them as the sole diet of their offspring in the nest. Adults are fueled by nectar and pollen, hence their dual importance to gardeners: controlling insects that damage plants while aiding in the pollination of the flowers they visit.
Trying to keep track of her in order to possibly discover her nest, I found her alighted on a leaf of Joe Pye Weed adjusting her load. Previously, upon capturing this prey, she quickly administered a series of stings to paralyze it, making it possible for it to be delivered as inert cargo to the nest and rendering it safe to inhabit the nest cavity with her tiny egg. (Imagine a softball placed next to a sofa for size comparison.) Her body, like that of all hunting wasps, is adapted to the transport of their specific prey, but the loads are nonetheless awkward and heavy, some weighing more than the wasp itself and which in some cases have to be dragged overland to the nest site. It is sometimes a fantastic feat of endurance and of instinctive perseverance.
I had no luck tracking the wasp any further, but I did find myself suddenly seeing this process from a new angle.
In my reading on this subject over the years the life cycle of these particular wasps has become pretty familiar to me, and two bits of data from that reading struck me. Following the hatching of the egg, the larva proceeds to consume the provision left by the mother completely. From that single meal throughout the entire metamorphic period - in total lasting up to ten months - the maturing larva does not pass any waste into the chamber or cocoon. This function starts only after emergence in the adult form. Essentially, the wasp winds up containing every single molecule of the caterpillar. In a manner of speaking, then, the female wasp, by supplying a copy of wasp DNA via her egg, has transformed a moth caterpillar into its own future predator.
I don’t present this as a metaphysical construct, but as an amazing and somewhat unusual example of the principle of conservation of energy running at very close to 100% in a biological system.
Not all hunting wasps are this efficient. The larva of those that hunt adult crickets and other hard-bodied prey do not consume the brittle structures such as wings and carapace shells, but though the conservation rates are slightly different, the idea is the same. This family of wasps and their specific prey are part of a very tight and interesting closed loop.