In Praise of Dead Old Trees

What to do with that dead tree in your yard? In a forest even a dead tree has its place providing homes and food to a variety of wildlife, what about the one in your property? You could leave it standing instead of cutting it down to the ground. You may have to remove some of the branches for safety reasons and keep only the trunk and main branches. Of course your neighbors and visitors may frown upon such untidiness. What can you say to them? You may tell them that it is an abstract sculpture. A dead tree isn't lacking in beauty but we are so obsessed with tidiness and the manicured look that it takes a readjustment of our esthetic vision to accept such a sight. Look at the architecture of the branches, the subtle hues of the weathered wood, the contrast between its stark lines and the exuberant greenery of the rest of your yard and you will begin to notice that it adds an interesting note to the whole.

In addition to its esthetic value a dead tree can become a home to numerous valuable pollinators, native bees that take advantage of the holes drilled by beetle larvae; also a dead tree may be very beneficial to woodpeckers, which may even prefer it to your live trees and leave them alone. And remember that when you are leaving that dead tree in your yard you are not really doing the pollinators and woodpeckers a favor but allowing them to have what is legitimately theirs. This is the way of Nature, all these creatures contribute to the ecological balance.

If you want to help the native bees even further, you can drill a few holes in the dead wood, they should be about the width of an ordinary pencil (they can be a little wider or a little narrower, there are so many species of bees that they come in several different sizes). The holes should be about six to eight inches long, slightly slanted upwards to protect them from the rain and they should face south or south east so the sun warms them up in the morning. I hope that next spring you get a few tenants in your bee condo.

Food Chain in the Milkweed Patch

Common milkweed. © Beatriz Moisset

The common milkweed teems with life. Numerous insects feed on leaves, stems, and roots or sip nectar from their flowers. It is ironic that a plant so well protected by powerful toxins and sticky sap behaves like a magnet for a large assortment of creatures. The best known dependent of the common milkweed is the monarch butterfly, but there are many others that deserve our interest. Many species have found ways to overcome the defenses of this plant. They have developed resistance against the toxic cardenolides and methods to avoid the milky sap.

The herbivores are in turn eaten by other insects or spiders, which may fall prey to still other carnivores. It is worthwhile to examine one of these so called food chains or food webs.

Oleander aphids on common milkweed. © Beatriz Moisset

One milkweed feeder, the oleander aphid, has become incredibly common in recent years. This bright yellow-orange aphid was accidentally introduced in this country with oleander plants, widely used in ornamental gardening. It established itself successfully and became adapted to milkweeds. It multiplies in huge numbers near the end of the season. It can do so because females reproduce parthenogenetically, that is without help from males.

Parasitized or mummified aphids. One wasp left the corpse through a round hole. © Beatriz Moisset

This aphid has few enemies. One of them is a tiny parasitic wasp. The mother wasp lays one egg inside a growing aphid and the larva completes its entire life cycle inside the unfortunate host. By the end of the aphid's life, it becomes dark, rounded and dried up. We call that a mummy. The fully grown wasp cuts out a round hole and emerges ready to start parasitizing other members of the aphid colony. It isn't easy to see the wasps, but almost every aphid colony has some of these mummified bodies. So you know that the parasitic wasps have been around.

Parasitic wasp. © Beatriz Moisset

Lacewings, lady beetles and syrphid flies also feed on aphids. Their stories are worth telling but we'll let them be for now.

The food web does not end there. Not surprisingly, many predators visit the milkweed patch in search of animal food. Parasitic wasps seem to be a delicacy among some flies. I have found members of two different families of predatory flies dining on the wasps.

Robber fly (Taracticus octopunctatus) feeding on a parasitic wasp. © Beatriz Moisset

One is a member of the family of robber flies, Asilidae. The name describes the members of this family well. They are seen pouncing mercilessly on their prey. One of them is Taracticus octopunctatus (no common name), a slender, hunchbacked fly with large eyes.

Long-legged fly feeding on a parasitic wasp. © Beatriz Moisset

Another one is a longlegged fly, Condylostylus, a shiny metallic green fellow, with long skinny legs. Parasitic wasps are part of its menu.

I marvel about this food preference. Evidently, these flies look down on the most abundant food nearby, the aphids, and go for the far less common parasites. Perhaps, the latter have less cardenolides than the aphids and this is why the predatory flies prefer them as food.

Longlegged fly caught by a spider. © Beatriz Moisset

A second layer of predation is added to the one just described. A spider feeds on a longlegged fly. We can summarize this food chain this way:

Milkweedaphidparasitic wasppredatory flyspider

Will a bird sweep by and eat the spider? Will it in turn fall prey to a hawk or a snake? How many steps can be added to this food chain? Common milkweed feeds many members of the wild life directly and indirectly. The links of this food chain are numerous.

More on milkweed dependents and visitors

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2014

Hidden Life on a Pear Tree

Bradford pear in bloom, attracting numerous pollinators

© 2014 Beatriz Moisset

Spring finally arrived, although a little later than usual. At the end of April, the Bradford pear trees in front of the Abington Library were in full bloom, white clouds against a sapphire sky. Hordes of little bees eagerly visited the sweet flowers.

Pollinators were not the only visitors to the trees. Surprisingly, life was also present in places you wouldn't think to look at. A cluster of bright yellow dots in a bark's crevice caught my eye just by chance. Afterwards, I began to see many similar clusters, partially hidden by the bark's irregularities. I knew them as lady beetle eggs, so I wasn't surprised to see some adult lady beetles engaged in romance or in search of potential nurseries for their babies.

Lady beetle eggs

© 2014 Beatriz Moisset

 A solitary green aphid painstakingly climbed the tree trunk, probably in search of tender shoots to feed on its juices. What was it doing so far from its traditional food? Perhaps, it had fallen to the ground and, obstinately, was engaged in the arduous voyage back to distant branch tips.

I puzzled at the lady beetles' choice of egg-laying sites. The tree trunk may offer refuge for the eggs, but not food for the newborns. The tiny larvae would have a long way to go to find nutritious aphids. Perhaps, just like the lost aphid, they could manage the perilous trek successfully.

I visited the trees a week later. They were still blooming, although slightly past their peak. I looked for the lady beetle eggs and found many of the clusters still in place. Some had darkened, a sure sign that the larvae inside would soon emerge, hungry for aphids. Others had become food for unknown predators and were gone.

An incipient aphid colony

© 2014 Beatriz Moisset

 Once again, I wondered where they would find food and looked at the new growth, the clusters of flowers which were already beginning to leaf out. Aha! Just as I suspected, the green aphids were there, small colonies of young and adults, wingless and even some winged ones. I would have never noticed them if I hadn't suspected their presence because of the lady beetles.

Aphids have a way of multiplying at great speed. One female can produce many babies in a mere week and the babies start reproducing in an equally short time. The small colonies I observed would become huge by the time the new leaves reached full size. They would be numerous enough to damage the new growth.

Aphid in search of food

© 2014 Beatriz Moisset

Would something keep the aphids in check? The mentioned lady beetles had their job cut out for them. But they would need lots of help and I was pleased to see other aphid enemies. I caught a glimpse of a parasitic wasp. These tiny wasps lay their eggs inside aphids and their larvae feed and kill their hosts in the process. Another great helper became apparent later on, on further observation. Some minute greenish grubs were thrashing about in the midst of the aphid colony. A syrphid fly had chosen this place to lay her eggs. The recently emerged blind and apparently helpless larvae were busy devouring their favorite food, juicy aphids. They grow fast on this nutritious diet and soon metamorphose into small flies, ready to lay more eggs.

Syrphid fly maggot feeding on aphids

© 2014 Beatriz Moisset

 The accidental sight of the lady beetle eggs led me to the related findings, aphids and their predators—an entire mini-ecosystem well hidden in bark cracks and flower clusters of a pear tree. A month later, I visited the trees again and found no traces of this entire food chain. The stems appeared too tough for the aphids; the winged ones had moved elsewhere. The lady beetles and other predators also took their leave in their perennial search for nourishment.

Aphids in the web of life

List of articles

Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2014