Riding the Great Lacuna

by Carl Strang

One of the many little mysteries I puzzle over is the spotty local distribution of field crickets. We have two species, the spring field cricket and the fall field cricket, in northeast Illinois. They look alike, sound alike, and are active in different parts of the season. Though they prefer much the same habitat, and more often than not occur together, sometimes one of the two species (usually the fall field cricket) occurs alone.

Green circles mark DuPage County locations where I have found both spring and fall field crickets. Blue circles indicate where only spring field crickets occur, and yellow circles mark spots exclusive to fall field crickets. The red area and blue star are explained below.

You can see that in east central DuPage County I found only fall field crickets through 2010. The yellow circles mark York Woods Forest Preserve (the northernmost circle), and in a row from east to west: Fullersburg Woods, Mayslake, Lyman Woods and Hidden Lake Forest Preserves. Together they seem to define a space, or lacuna, where spring field crickets may be absent. On Monday I rode my bike between these locations, listening as I went for field cricket songs. Though much of this area is occupied by gated residential communities, the city of Oak Brook also maintains a fine system of bike paths which allowed me to zigzag through much of the zone marked in red on the map.

I found mainly mowed lawns, residences, woodlands and businesses (including the McDonald’s corporate headquarters and “Hamburger U”), but there were plenty of places just like ones in which I have heard numbers of spring field crickets elsewhere, with unmowed grasses or mixed grasses and forbs. In all that area, though, I heard only two crickets singing, close together in the location marked by the blue star on the map. That spot marks the northern extent of a zone I should investigate further, between the Fullersburg and Mayslake preserves.

Still, it seems the lacuna is indeed largely empty of spring field crickets. Next steps will be to find how far the boundaries of this area extend, and to look at old aerial photos for clues as to why this region might be different, keeping in mind that fall field crickets are present. I may repeat yesterday’s bike ride in the late summer or fall to see if fall field crickets occur in the spaces between those preserves.

Field Cricket Transition Time

by Carl Strang

In an earlier post  I introduced a pair of sibling species, the spring and fall field crickets. Now that we are in mid-July, we have reached the time of transition between the two. I am interested in the fact that I have not always found both species together. This June I put some time into visiting locations where previously I had noticed only fall field crickets. I wanted to determine whether those places also held the spring species. Here is the map of my data after that survey.

Field cricket map

In this map, green dots mark places where I have found both species. Yellow dots indicate locations where there are only fall field crickets. Blue dots mark places where I have records only for spring field crickets. These all are locations I need to check in August or September, because I have not looked for fall field crickets there. I indicated that ambiguity by placing black dots over the blue dots’ centers. So far there is not much to say, apart from the fact that there is a cluster of preserves in east central DuPage County (Fullersburg Woods, Mayslake, and York Woods) where only the fall field cricket can be found. Yesterday I heard the first field cricket of the year at Mayslake. This marks the season start for the fall field cricket. If I can find preserves with only spring field crickets, I’ll be able to monitor precisely the local seasonal transition between the species. I also will seek an explanation for the resulting county distribution.

Gypsy Moth Caterpillars

by Carl Strang

Earlier I described gypsy moth egg masses . These hatched in May, and the caterpillars have been busy. The larval gypsy moth is distinctive.

Gypsy moth 4JEb

This caterpillar, about an inch long, I photographed at Mayslake on June 4. It is hairy, has rows of blue and red spots on its back, and (not so visible in the photo) a mottled yellow and black head. The entire package reminds me of a Chinese parade dragon. There would be no problem if there were just this one, or a few. Unfortunately their populations build to the thousands, enough to strip some trees of their leaves. On June 13 I visited York Woods, where several oaks were defoliated last year. Though some leaves looked well chewed,

Oak leaves chewed York b

I saw no trees that appeared in danger of being defoliated this year.

Oaks 13JE York Woods 1b

Earlier in the season, helicopters sprayed a bacterial disease at York Woods and other spots where there was danger that gypsy moths would defoliate trees. I saw one dead gypsy moth caterpillar that appeared to have been killed by this disease.

Gypsy moth killed York b

The bacillus attacks all moth and butterfly caterpillars, and so the decision to spray is not made casually. As I understand it, the spray is used to protect hot spots as long as these are few and local. Once the gypsy moth population builds to the point where they are abundant and universal, that spray will be discontinued (except, perhaps, in certain high use and high quality areas) and hope will shift to a fungal disease, predators and insect parasites to limit the harm done by the caterpillars. The usual pattern is a few years of unpleasantness and the loss of a percentage of trees (mainly ones weakened by other conditions), after which there is a permanent presence of diseases and parasites that keep gypsy moths within limits.

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