Snags

While most wildlife get the things they need from living trees, there are still a large number of animals that rely heavily on dead trees. In nature there are always trees that come to the end of their lives, and they continue to provide food and shelter long after they have stopped living. Trees are fantastic in that way. In a living tree, most of the wood is unavailable for other organisms, while in dead trees it becomes a relatively good source of food for wildlife. Of course, it is true that a dead tree is more likely to topple than a living tree. If you think that a tree could come down on your house, you may still be able to save wildlife (and your money) by only cutting down part of the tree. Unfortunately, humans have gotten into the habit of just removing dead trees without any consideration given to the environmental impact. Removing dead trees lowers the density of bird populations.

 

I have a snag in my suburban garden. The tree had to come down due to serious injury in a storm but I left a stump that was 11 feet high. I considered the maximum height allowable by looking at its position in the garden relative to the fences and the building structures. Within 2 years, unusual insects started showing up in the garden. Horntails are large ichneumonid wasps that do not sting. They lay eggs in the crevices and the larvae that hatch burrow inwards and feed on the wood. Older trees with thicker trunks have a lot more value to wildlife. Our preconceived notions of gardens that they should be clean and tidy often make us think that a snag would be ugly; however, you will love watching the wildlife that shows up in your garden to take advantage of your snag.

	Horntails are fairly big ichneumon wasps. They are completely harmless to humans and help speed up the decay process in dead trees.

Many insects have parasites or parasitoids. In this case, horntail larvae are fed upon by parasitoid wasps called Megarhyssa that have very long ovipositors used for depositing eggs. They have to locate a larva of the horntail underneath the bark and then drill into the wood to reach it.

	Megarhyssa macrurus is a parasitoid of horntails. They only feed on horntail larvae and without snags, these stunning insects would not have a habitat. The exceptionally long tail seen here is an ovipositor capable of drilling into wood to lay an egg on a tunneling larva beneath the surface.

 

Snags help wildlife in the following ways:

1) They are a source of food for many insects and other invertebrates. The tunnels made by beetle larvae provide nesting sites for many solitary bees.

2) The insects in these trees are a source of food for many birds. If you leave a tree to decay naturally in your garden you may well be rewarded with the appearance of a pileated woodpecker. These birds are one of the most impressive in North America.

3) Woodpeckers excavate holes in these trees for nesting. When they leave (and they only tend to use a hole once), the holes get used by other birds, racoons, flying squirrels and bats. The holes provide nesting sites and winter roosting sites to avoid inclement weather. The importance of these holes for the survival and propagation of bird populations should not be underestimated.

4) Several birds of prey use snags for perching as do many smaller birds.

5) As the snag continues to rot, it will be used by amphibians and smaller mammals.

	Snags often are visited by yellowjackets. They scrape the wood and then fly back to the nest.