Category Archives: Environmental

Caddisfly Home Decorating

I was snorkeling in shallow water in a small lake in central Massachusetts today, and saw an interesting creature. What caught my eye was that a small section of the sandy gravel on the lake bottom was moving. It scooted forward about an inch (2.5 cm) and stopped. Then it did it again. I picked it up gently and turned it over to investigate. It was about 3/4 of an inch (2 cm) long and about 1/2 an inch (1 cm) wide. It was made of grains of sand and gravel glued together. Attached underneath was a small tube. The creature who lived in the tube had withdrawn and couldn’t be seen, but I knew what it was: the larvae of one of over 4,000 species of caddisflies. Most caddisfly larvae construct houses, which they use for disguise and protection. Each species uses characteristic materials and design. The resulting shelters range from a small tube of reed or grass, to houses constructed out of sand in the shape of a snail shell. Other caddisflies actually glue tiny snail shells together. Most caddisfly larvae graze on algae and other plant material. Eventually, they leave the water and metamorphose into a somewhat moth-like adult. Caddisflies are, in fact, related to butterflies and moths. The pictures below show some of the diversity of caddisfly larvae homes. Unfortunately, none looks quite like the one I saw, and I didn’t have a camera, but a couple show homes constructed of gravel.

Caddisflies are often used in evaluating the health of streams. Most species are not tolerant of pollution or silted water, so to find a healthy collection of caddisflies in a stream is a good sign.

What I find most amazing about caddisflies is that they are able to construct such clever, effective and attractive homes with such a tiny brain. Incredible.

 

Are Sharks Immune to Disease and Cancer?

The Question: I recently read that sharks are immune to all disease.  Is this true?

Submitted by: Marion F., Somerville, MA

The Short Answer: No, it’s not true. Sharks get bacterial infections, viral infections [see comments], and they suffer from parasites, in short, the entiShark_Silhouette - wikimedia.jpgre suite of infectious diseases from which all animals and plants must protect themselves. Sharks also get cancer, contrary to another widely disseminated myth.

More Info:
The claim that sharks don’t get disease or suffer from cancer is mostly spread by advertisements for shark cartilage as a dietary supplement. These supplements claim to prevent disease or cure cancer, but none has ever been shown in rigorous medical tests to protect people from disease. Tumors rarely infiltrate into cartilage, in any vertebrate whether a shark or a person, and cartilage seems to have some ability to inhibit the growth of blood vessels. Since a growing tumor needs blood vessels to continue to expand, there have been attempts to develop “antiangiogenic” drugs that fight cancer by limiting growth of new capillaries. Ground cartilage, whether from sharks or cows, shows some antiangiogenic effect in the laboratory, but has not shown any benefit in actual people. But shark cartilage sellers have connected the fact that the skeleton of a shark is entirely made of cartilage with the antiangiogenic properties of cartilage to claim that this protects sharks from cancer. It just isn’t true. The truth is that while we do know for certain that sharks get diseases and cancer, we don’t know at what rate. Sick sharks probably get eaten or fall to the bottom of the ocean to decompose. They would rarely be available to be counted. Sharks that are harvested by fisherman do occasionally show infectious disease or cancers. No one has done a comprehensive survey of sharks to know whether they have high or low rates of illness. Even if sharks are particularly free from disease, that wouldn’t necessarily mean shark cartilage has any value as a treatment for human disease. And the tests that have been done have not shown any value over a placebo. shark snout - wikimedia.jpg

The Interesting Science: The immune system of sharks is very much like ours. We have what’s called the “innate immune system” which is somewhat hardwired to fight generalized intruder microorganisms and parasites. The innate immune system can respond over long periods of time through the mechanism of natural selection to adapt to new diseases. We also have an “adaptive immune system” (also called the “acquired immune system”) that adapts in real time to new intruders. This is the familiar system of antibodies and white blood cells that gets the most discussion in terms of diseases such as flu, the common cold, and AIDS. It was once thought that vertebrates like sharks, bony fish, amphibians, reptiles, birds, and mammals were the only animals that had an adaptive immune system. But recent discoveries have shown that lampreys and hagfish, fish that split off onto their own evolutionary branch early in the history of vertebrates, have a different system of generating antibodies and adapting to fight new viral and bacterial threats. And it appears that Mustelus_asterias - wikimedia.jpgother animals from snails to fruit flies may also have adaptive immune systems that work differently from ours, but accomplish the same goal of recognizing and attacking new microbes and viruses.

The Environmental Message: Shark populations are plummeting around the globe, in large part due to fishing for shark fin for shark fin soup, and for cartilage for shark cartilage supplements. As top of the food chain predators, shark numbers have never been as high as a fish like cod. Sharks also reproduce slowly. Unlike a cod, which can lay millions of eggs, many sharks lay only a few hundred in the average lifetime. What this means is that harvesting sharks is generally not sustainable. There aren’t enough of them to start with, and they can’t rebuild their populations rapidly.

References:
Shark Cartilage, Cancer and the Growing Threat of Pseudoscience. Ostrander GK, Cheng KC, Wolf JC and Wolfe MJ. Cancer Research, 64, 8485-8491, 2004.

Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial. Cancer, Jul 1;104(1):176-82. 2005.

Added in Dec. 2013:  First reports of proliferative lesions in the great white shark, Carcharodon carcharias L., and bronze whaler shark, Carcharhinus brachyurus Günther. R. Robbins, B. Bruce, A. Fox, Nov. 2013, Journal of Fish Diseases.

Ladybird, ladybird, fly away home

The Question:
Some years we have many ladybugs, other years just a few. This spring they have been inside the house. When just a few, I sort of like them. When an infestation, they can be a nuisance. Can you tell me more about the life cycle of lady bugs?

Submitted by: Prue, MA

The Short Answer: The ladybug (ladybird in most of Europe) that has been invading houses for the last 20-30 years across most of North America and Europe as well, is the Asian Ladybird Beetle, Harmonia axyridis. As figure 2 shows, they are highly variable in color and number of spots. One way to identify them is the characteristic white areas and the distinctive M or W on the prothorax, right behind the head (figure 1). This marking is fairly clear in all but the blackest variations.

As their name implies, the Asian Ladybird Beetle was originally native to Russia, China, Korea, and Japan. It was introduced at various times in the 20th Century in North America, South America, Europe and Africa to control aphids on crops such as apples, pecans, and soybeans. Sometime between 1970 and 1990 populations began to grow rapidly in the United States. Today, although Harmonia axyridis is still used by farmers to control aphids – and is still effective in that job – it also considered an invasive species that threatens our 500+ native species of ladybugs. It is now the most common ladybug in North America. Figure 3 shows the life cycle of the beetles from mating (upper left) to metamorphosis into an adult (lower right).

More Info: In its native habitat, the Asian Ladybird Beetle spends the winter in large groups in cracks in rock cliffs and other open rock formations. It is also attracted to people’s homes. But the number of beetles is nowhere near the numbers reached in North America and Europe, where a single home can attract a few beetles, or a few hundreds, or millions of beetles. In small numbers, the beetles are harmless, but in large numbers, they can be annoying and destructive. They release a smelly yellow “blood” when they feel threatened. This hemolymph fluid can leave a difficult-to-remove stain and odor. The beetles can also bite, and although the bite isn’t particularly painful or harmful, people have reported being swarmed by the beetles outside their homes. Some people also appear to be allergic to the beetles and a large infestation can trigger allergy symptoms.

It has been widely reported that light colored houses attract the beetles, but a study in Ohio found no difference in house color between houses with large infestations and those without. There seems to be a tendency for them to be attracted to houses with contrasting colors, and the proximity of woods makes it more likely for a house to become an attractive target. There is also some evidence that they are attracted by the scent of locations where beetles have been in prior years.

The Ohio study showed a very clear pattern of when the beetles move. They tend to swarm on warm days after cold days. In Ohio, they move throughout the fall any time there is a day of 65oF (18oC) within a couple of days after freezing temperatures.

There is no one easy solution to protecting your house from the beetles. It helps to seal up all cracks with caulking, tight windows and doors, etc. This has the added benefit of making your house more weather tight, of course, so it’s probably worth the effort. It’s nearly impossible to find every crack small enough to eliminate the beetles entirely, but this process can reduce them greatly. The insect repellent DEET, when sprayed around windows and doors, can reduce the number of beetles. Indoors, the most effective control is to vacuum them up. If you put a nylon sock into the vacuum tube and tape it in place, you can collect the beetles without having them go into your vacuum bag. Don’t release the beetles outside your house, or they may just come back in.

The Asian Ladybird Beetle is a classic example of the danger of introducing a generalist predator to control agricultural pests. The larvae of the Asian Ladybird Beetle not only eat the aphids they were meant to control, but also the eggs, larvae, and sometimes the adults of other ladybugs and other insects as well. Because they taste bad, few birds will eat them, although the Grey-Headed Woodpecker and the Eurasian Nuthatch, two Eurasian species, seem to be exceptions. Most predators and parasites that might be introduced to control the Asian Ladybird Beetle are just as happy to prey on our native ladybug species as well. So until some natural control arises, due to disease or adaptation of predators, we are probably stuck with large populations of Harmonia axyridis. If we could figure out how to keep them out of our houses, most of us would probably never notice the growing population of Asian Ladybird Beetles, and sadly, we probably wouldn’t notice the loss of our native ladybugs either.

Farmers still value the Asian Ladybird Beetle’s ability to protect crops from aphids, although they can be a problem for grape growers because of their tendency to feed on damaged fruit. They will often get into grape bunches and when the grapes are harvested and processed, the beetles are crushed, releasing their noxious fluid, which can taint grape juice or wine with an unpleasant smell.

Trivia #1: A ladybug is technically a beetle, not a bug. Scientifically, bugs are members of the insect order Hemiptera. The Hemiptera include insects with sucking mouthparts such as aphids, cicadas, leaf hoppers, and shield bugs. True beetles on the other hand, are members of the Coleoptera. One of the distinguishing characteristics of the true beetles is sheathed wings. If you ever see a ladybug lift off, you’ll noticed that the hard red and black sheaths move aside to let the hidden wings carry the beetle away.

Trivia #2: There is a children’s poem featuring the ladybug (or ladybird beetle):

Ladybird, ladybird, fly away home
Your house is on fire and your children are gone
All except one, and that’s Little Anne
For she has crept under the warming pan.

The Interesting Science: I was unable to find any research on why there are more beetles some years than others. Variations in the population levels of their prey and in climate probably play a role. Most studies of population fluctuations of predators are on big predators such as cats, canids (wild dogs, wolves, foxes, etc.), and bird raptors. While ladybugs are predators, they also have the ability, common to insects, to multiply rapidly. Mammals and birds are limited in how fast they can increase their numbers to take advantage of a booming prey resource, but ladybugs probably react much more quickly. This may lead to larger boom and bust cycles for ladybugs, than for larger predators, but again, I haven’t seen any research on this.

References:

Current and potential management strategies against Harmonia axyridis. Kenis M, Roy H, Zindel R, Majerus N. BioControl 53(1), 235-252, 2008.

Multicolored Asian Lady Beetle (Harmonia Axyridis) as a nuisance pest in households in Ohio. Heulsman M, Kovach J, Jasinski J, Young C, Eisley B. Proceedings of the 4th International conference on Urban Pests, Jones S, Zhai J, Robinson W, editors, 2002.

Bad side of a good beetle: the North American experience with Harmonia axyridis. Koch R, Galvan R. BioControl 53, 23-35, 2008.

Where Does Trash End Up?

I was very much affected by these photos in the latest issue of Audubon Magazine: http://www.audubonmagazine.org/onepicture/onepicture1003.html. For some reason, they reproduced it in a small, low-res format. To see a better version, go to this pdf and go to page 21 of this presentation: http://faculty.philau.edu/AshleyJ/Philly_U_MD_Bamford.pdf (if you want to get really depressed, read the whole presentation.)

If you’ve ever wondered whether a little trash makes any difference, this picture gives a moving answer. The bottle caps, cigarette lighters, and hundreds of other pieces of trash that killed this albatross may have come from half way around the world. Albatross will scoop up just about anything they see on the surface of the ocean because in pre-plastic days, virtually anything floating on the ocean was food. Also, apparently, flying fish lay their eggs in long strings attached to floating objects, and albatross feed on them by scooping up whatever they see floating. Then they go back and regurgitate to their chicks. Unfortunately, all the plastic junk the parents have ingested ends up in the chicks. In this case, it was enough to kill the chick.

These photos are a tragic demonstration of the interconnectedness of our environment. Every bottle cap or plastic bag we throw away on the sidewalk can end up washing into a storm grate, into a river, out into the ocean, and eventually into the gut of an albatross chick.