I like damselflies quite a lot because of their visual appeal, and I found an interesting business that sells nymphs. No where near as pretty, their appetites for mosquito larvae make them appealing as well, given there’s a wetland on our property that surely breeds mosquitoes. (FTR, these damselflies are native to our area, so no introduced species worries. The company is based nearby too). I’d like to buy some nymphs for both reasons.
BUT the wetland is only truly wet from September to June. In July and August it’s often only damp, if that, unless it’s unusually rainy those months. Would putting them in there kill them once it dries up? Or would they burrow into the ground to stay moist like some creatures do? They’re nymphs for up to two years, so this is a major concern.
There are already many that appear on the property, but there’s also a river across the road, so I can’t take this as evidence that the wetland is an ideal condition for them…
Missed the edit button: many adult damselflies appear in the yard already, I meant, not nymphs.
Based on your description, the wetland likely already has standing populations of dragonflies, damselflies, aquatic beetles and true bugs that keep the mosquitoes in check. The nearby river may or may not be contributing significantly to the number of adult Odonates (dragonflies and damselflies). If the river is slow and has lots of aquatic vegetation or backwater areas, there may be good habitat for them. Swift water and rocky substrate is generally not suitable habitat.
If you have mosquito problems on your property you should check for smaller, more ephemeral sources of water in which mosquitoes can breed such as tires, buckets and cans, or clogged gutters.
Aquatic insect voltinism (number of generations per year, or the number of years to complete the life cycle) varies by climate, so an insect that takes two years to mature in a cold climate might take only one year in a warmer climate.
Your wetland probably already has a decent community of insects that are adapted to the hydroperiod (seasonal pattern of inundation and drying) of wetlands in your region. Typical pond damselflies (e.g., Enallagma sp.) generally do not require more than one season to mature in New Hampshire.
I’m no where near an expert, but wouldn’t introducing new damselflies be rather pointless? They already exist in your area, so if they could survive in the place you live, they would already be there… Adding more won’t increase the number you have in your vicinity, it will just temporarily lessen the amount of food for all and thus starve out the surplus so that it balances out again. I.e. no change.