Image courtesy MDC
You’ve likely heard that if you want to help monarch butterflies, you should plant milkweeds. But what do you do if you want to help federally endangered Hine’s emerald dragonflies? Easy. Plant devil crayfish.
As bizarre as it may sound, “planting” devil crayfish is a necessity if you want to create habitat for Hine’s emerald dragonflies. To understand why, you need to know a few peculiarities about these beautiful but rare insects.
Like other dragonflies, Hine’s emeralds are “aquatic insects.” Adults lay their eggs in the water, and the larvae that hatch from those eggs stay underwater until they develop enough to leave and molt into winged adults. (For Hine’s emeralds, this can take up to five years.) But unlike other dragonflies, Hine’s are picky about the waters they call home.
Hine’s emerald dragonfly larvae only live in groundwater that flows through dolomite bedrock before surfacing to form rivulets, exceptionally shallow, narrow, slow-flowing bodies of water. Even then a Hine’s emerald needs an additional feature, the final and most critical factor of all: a devil crayfish burrow.
For reasons still unclear, Hine’s emerald dragonfly larvae only live in devil crayfish burrows. They won’t live in other underground formations, and they won’t use burrows of any other crayfish. Adult Hine’s emeralds won’t even breed in a habitat if devil crayfish aren’t there as well.
One reason for this requirement may be that these crayfish are “primary burrowers.” They build complex burrows deep enough to reach underground water tables below the frost line, which means the water doesn’t freeze. This source of cold open water is critical if Hine’s larvae are to survive winter.
So if an area might be good habitat for Hine’s emeralds but is missing devil crayfish (or is currently Hine’s habitat but has few devil crayfish burrows), “planting” crayfish is essential. This is where the Forest Preserve District’s new devil crayfish captive-rearing program comes into play. The goal is simple: Raise devil crayfish in captivity and release them as juveniles in the wild to create breeding grounds for Hine’s emerald dragonflies.
It starts by collecting “gravid” female crayfish (those carrying fertilized eggs) in the wild. Since devil crayfish mate in early spring, the best time to do this is April through early June.
The females go in a special tank at the Forest Preserve District’s Urban Stream Research Center, where they’re fed and kept comfortable and clean. The center is a one-of-a-kind facility for studying and rearing aquatic animals such as crayfish, dragonflies and mussels.
The crayfish eggs start out as small dark balls, which the female carries under her tail. In two to three months they change color and develop eyespots. Eventually they become free-swimming juveniles and will, a few at a time, leave the female for short periods. As they get older and venture further away, it’s time to remove the female from the tank. The more time her young spend away from her, the less she’s able to sense them under her tail when they return, which means she may begin to eat them, thinking they’re prey.
With the female gone, the juveniles are fed and kept clean until it’s time to “plant” them (aka release them) into appropriate forest preserve habitat.