“Stayin’ Alive”: Tricks Insects Use
By Bruce Rottink, Volunteer Nature Guide
This Naturalist Note was deleted from the website by a computer crash in 2014. This is a slightly modified version of that original note.
As my friend Roland says, “Everything in the forest is someone else’s lunch.” Insects are a prime example. In the forest, insects are a high protein meal for innumerable species of birds, spiders and other insects. Over thousands of generations, the insects found in Tryon Creek State Natural Area have developed lots of tricks to help them stay alive.
One widespread trick used by many insects is to be the same color as their habitat. This is one type of camouflage. If you are an insect that crawls around eating leaves, being green is a good choice. One example is this caterpillar recently found on one of Tryon Creek’s vine maples (Acer circinatum). The prolegs, the fat fleshy “legs” on the rear part of the caterpillar, are common in the insect order Lepidoptera, which includes butterflies and moths. The six true legs of the insect are relatively small; some can be seen just in back of the head, which is on the left in this picture.
Another option is staying out of sight, sometimes in odd ways. An early summer inhabitant of the Tryon Creek forest is the spittlebug. The spittlebug is the nymph (the immature stage) of an insect called a froghopper, in the insect superfamily Cercopoidea. The immature froghoppers suck nutritious juices out of a plant and create a blob of foam for protection.
At first glance, a predator might not think a blob of foam contains a tasty snack, and just pass it by. But even if the predator decides to check it out, the foam has two more layers of defense. First, you can’t tell exactly where in the foam the insect is hiding so the predator might just give up. Second, it is reported that the foam tastes very bad. The foamy home also helps the young insect by helping reduce water loss by the nymph, and is a layer of thermal insulation against both heat and cold.
The nymph inside the foam is pretty cute in a bug-gy sort of way. This one was found on a salmonberry (Rubus spectabilis), but I have also seen several on stinging nettle (Urtica dioica). Based on experience in my garden, they will attack a wide variety of plants.
Another secretive insect life style is that of the leaf miner. These insects have it made. The female insect lays her eggs on the leaf, and upon hatching, the larvae burrow into the leaf. They spend their entire larval life inside the leaf where they eat only the most nutritious parts. It is like you living inside a giant hamburger, eating your way from one place to another.
In the process of munching through the leaf, the insect kills lots of leaf tissue, which eventually turns brown and marks the course of the leaf miner’s journey. As you can see in the thimble berry (Rubus parviflorus) leaf below, the larval track starts out very small (upper right), and increases in size as the larvae grows bigger and works its way through the leaf. At the end of the larval stage, it emerges from the leaf, often leaving a noticeable hole. (Not all the holes in this leaf are associated with the leaf miner.)
Many different kinds of insects have developed the leaf mining lifestyle, including various moths (Lepidoptera), beetles (Coleoptera) and flies (Diptera). At Tryon Creek, I have commonly seen these on a wide variety of plants, including jewelweed (Impatiens capensis) down by the creek.
Yet another protection lifestyle is used by the leafrollers. Unlike the leaf miners, which represent a variety of kinds of insects, leafrollers are all the larvae of moths. These ambitious little larvae will roll up a leaf, tie it up with silken strands, and may either feed within the rolled-up leaf, safely pupate there, or both. As in so many other insect strategies, a rolled-up leaf is a great hiding place, and also must provide a certain amount of shelter from the elements. Worldwide, some leafrollers are important pests of agricultural plants as well.
The example below is on a salmonberry. Recently I’ve also seen leafrollers on elderberry (Sambucus racemosa), stinging nettle and jewelweed at Tryon Creek.
Viewed from the end, the rolled-up leaf is shown below:
When disturbed, they are reported to use a silken thread to lower themselves to the ground. However, this little guy apparently didn’t want to take the fall. It boggles my mind that this little larva could roll up a salmonberry leaflet. Nature is endlessly amazing!
While these insects might be at the bottom of the food chain, they’ve still found ways to stay alive long enough to create the next generation of insects!
There are reported to be more than 28,000 different species of insects in the Pacific Northwest. They have developed a huge variety of successful lifestyles. As you are walking through the forest keep your eyes open to see how many different kinds of insects you might encounter.
The Skeletons of Tryon Creek
By Bruce Rottink, Volunteer Nature Guide
Originally posted in August of 2013, this Naturalist Note was among several that were lost due to a computer glitch in early 2014. I’m re-posting so it isn’t lost forever!
Months ahead of Halloween, Tryon Creek State Natural Area is already swamped with skeletons! They’re everywhere! But these skeletons aren’t the bony remains of dead animals; they’re the nearly invisible outlines of dead tree leaves. At a time when the red alder (Alnus rubra) leaves should look like this:
Many look like this:
The red alder trees in the park and beyond are under attack by an outbreak of the alder flea beetle (Macrohaltica ambiens), a species native to the United States. The tiny black larvae of this beetle are the main culprits. These ¼-inch long gluttons hatch in late spring and start feeding. They only eat the soft parts of the leaf, leaving a leaf skeleton that consists of the tougher leaf veins. Under normal circumstances, these veins carry water from the roots up to the leaves. These veins also transport the sugars produced by photosynthesis in the leaf to nourish other parts of the plant like the trunk and roots. The close-up below shows the tree’s finely detailed plumbing system.
As devastating as the attack is, one can’t help but find some lacey beauty in these skeletonized leaves.
About early August, the larvae drop to the ground and pupate. After the 10-day pupation period, they emerge as adult beetles. As if the larvae hadn’t done enough damage already, the adult beetles then attack more alder leaves. They chew holes in the leaves, as seen in the following photo. Finally, the adults drop down into the debris on the forest floor and hibernate until spring. In the spring, the adults emerge, mate, and the cycle starts all over again.
The alder leaf beetle primarily attacks alders, but will sometimes feed on other trees like willows (Salix spp.) and poplars (Populus spp.). However, at Tryon Creek this year, it looks like the damage is confined to alders. This beetle is just one of a number of insects that “skeletonize” leaves of different plants.
Arborists have indicated that the alders will survive; no need to panic on that score. On the other hand, alder leaves normally stay green on the trees until quite late in the autumn. The beetle is robbing the trees of the opportunity to photosynthesize for a couple of extra months. The carbohydrates that the tree would normally create and store during this period will be missing! With lower food reserves in the spring, the tree’s growth will probably be reduced next year.
Expert opinion is that vigorous trees are less likely to be attacked. The beetles focus on vulnerable trees that are water stressed or otherwise in poor health. The number of beetles present in the forest varies dramatically from year to year. Perhaps this year’s outbreak is related to the extended dry period we are experiencing.
There is a lesson here related to global warming. Some trees will die because the climate gets too hot or too dry for them to survive. But in many cases, scientists have already found that climate change will stress the trees, and then the opportunistic insects and diseases which attack unhealthy trees will be death’s deliverymen.
A Living Stump
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
This article was originally written and posted in 2013, but vanished from the website during a computer crash in early 2014.
Most people come to Tryon Creek State Natural Area because of all the wonderful things they know they’ll find: majestic Douglas-firs, beautiful flowers and lots of birds. But sometimes, nature has surprises in store, which can both amaze and delight us.
One such amazing surprise is a large living Douglas-fir stump in the northern part of the park. A “living stump” sounds like a contradiction. The leaves or needles in the crown of the tree produce all of the tree’s food. Thus, you would think that once a tree is cut down, the stump is finished, dead, history. Mostly, that’s true, but that is not always the case.
What allows a stump to stay alive after the trunk and crown are removed? Root grafts! Unseen by human eyes, many trees form natural root grafts with other nearby trees of the same species.
Scientists have learned over the years that both water and nutrients can flow through these natural root grafts. If two trees are root grafted together, and one is cut down, enough water and nutrients can flow from the standing tree to the stump to keep the stump alive for many years. The response of the living stump is to try to heal over the cut surface where the trunk was severed.
The most common type of root grafting is between two roots of the same tree. Next most common is between two different trees of the same species. Root grafts between trees of two different species have been found, but they are extremely rare, and mostly occur between two species that are able to hybridize with each other.
Most often, a healing callus, which looks like a kind of scab, starts from the edge of the cut stump, and gradually grows towards the center of the stump. This callus is produced by the tree’s cambium which is a thin layer of actively dividing cells between the bark and the wood of the tree. This is a very slow process. In rare cases, this callus eventually caps the entire stump.
I found an impressive living Douglas-fir stump at TCSNA. The probable root graft partner of this particular living stump is a large Douglas-fir tree growing less than 6 feet away. The newly discovered living stump at Tryon Creek is remarkable on two counts. First, it is huge. The circumference of the stump is 9 feet, 4-1/2 inches. Secondly, the cut surface on the top of the stump is completely healed over. The red lines I’ve added indicate the top of the original stump. In all my 10 years of experience as a Research Forester, I have never seen a stump even close to this size that was completely healed.
As cool as this root grafting and living stump phenomenon is, this is not necessarily a positive thing for the trees. One of the best documented problems is that tree diseases are readily transmitted from tree to tree through these root grafts. The most famous example of tree diseases spreading through root grafts is Dutch elm disease that has devastated urban street trees in the eastern U. S. In Douglas-fir, diseases such as laminated root rot (Poria weirii) can also be transmitted from tree to tree via the root grafts.
If you would like to see one of Tryon Creek State Natural Area’s living stumps, it’s easy. There is a great example of a living stump near High Bridge. Starting at High Bridge, take the short (0.04 miles) trail leading to the North Horse Loop. At the junction of this short trail, and the North Horse Loop, look to the southeastern side of the trail, and there is a living stump, which is circled in red below:
What other oddities are there in the park? Next time you visit, keep a sharp lookout for strange things, and maybe you can discover Tryon Creek’s next natural wonder!
Tryon Naturalist Notes 