Photo by Kirk Nelson
Virile crayfish (Orconectes virilis) is a medium- to large-sized freshwater crustacean. It is widespread and abundant across North America. It is native to central United States and Canada, from Quebec to Tennessee in the east, to Alberta and Colorado in the west. It is introduced and considered invasive outside of its native range from coast to coast.
Virile crayfish prefer streams with rocky bottoms, moderate flow and turbidity, abundant cover, and stable water levels. They often use rocks, logs, or other organic debris as cover. They occasionally dig burrows into muddy banks, especially when water levels are low. To survive the winter, they migrate to deeper water that does not completely freeze and they become inactive.
Virile crayfish are identified by the dappled, olive-brown body with pairs of dark brown splotches on the abdomen; the shape of the shield (carapace) covering the front part of the body; and the broadly flattened, usually bluish claws.
Photo by Alfredo Colon
Long-tailed dance fly (Rhamphomyia longicauda) is a small, black, long-legged fly. It is commonly found from May to July in deciduous woods near water. The wings are long and black. The head is round with large bright orange or red eyes. On the female, the middle and hind legs have a fringe of long, black, bristly hairs.
Every evening around sunset, males and females collect in same-sex swarms. Females and fly up and down, the behavior that gives this family its common name “dance-flies”. Females cannot hunt for prey. They receive protein from males as gifts in exchange for copulation. They swallow air, filling and extending their abdomen outward, saucer-like, falsely signaling males that their eggs are nearing maturity. The long hairy legs wrap around the abdomen, making it appear even larger. Males are attracted to females that have largest swollen abdomens and hairiest legs. An individual will break off and join the other swarm to select a mate.
Photo by Alfredo Colon
Colorado potato beetle (Leptinotarsa decemlineata) is relatively small for a beetle but relatively large for a leaf beetle. Adults are ¼″ to 7 ⁄16″ long and about ⅛″ wide. The body is oval when viewed from above and dome-shaped when viewed from the side. The wing covers are pale yellow with five black lines on each side. The are no similar species in Minnesota.
Prior to European settlement, the Colorado potato beetle was found only in Colorado and neighboring states. The potato was introduced into North America in the 1600s and began to be widely grown in the early 1700s. By 1840 the potato reached the insects home range. By 1859 the insect had switched to the potato as its preferred host, and by 1874 it had spread all the way to the east coast. It is now present across North America, Europe, and Asia.
Colorado potato beetle is a serious crop pest to potato growers. The insect rapidly evolves resistance to chemical pesticides. Many insecticides that once successfully controlled the beetle are no longer effective.
Photo by Alfredo Colon
Four-lined plant bug (Poecilocapsus lineatus) is a small, soft-bodied, colorful, true bug. It is common in northeastern and midwestern North America, including Minnesota. It is easily identified by the bright yellow or green body with four black stripes and the orange head. It can be seen from May to July in meadows, gardens, agricultural fields, and around homes.
Four-lined plant bug is considered a pest due to the damage it causes to ornamental plants. Adults and larvae feed on the leaves of herbaceous plants, especially those in the mint and aster families. Leaf damage appears as small, 1 ⁄16″ or less in diameter, light or dark spots on the leaf surface. The color of the spot varies with the species of the host plant. The spots are collapsed leaf tissue which eventually falls out leaving small holes. Larvae cause more leaf damage than adults.
Photo by Dan W. Andree
Six-spotted tiger beetle (Cicindela sexguttata) is a small predaceous, tiger beetle. It is probably the most common species of tiger beetle in eastern North America, possibly the most common on the continent. It is found in the southern two-thirds of Minnesota. Adults and larval burrows are very often seen on paths in the woods. Six-spotted tiger beetle can be thought of as a woodland path species.
The head and body are shiny, iridescent, and usually metallic green, occasionally blue. Flashy tiger beetles (subtribe Cicindelini) are usually identified by the color and pattern of marks on their wing coverings. The common name of this species comes from white spots on the wing covers. There are usually six small spots, often eight, rarely ten, and occasionally none.
Japanese hop (Humulus japonicus) is an invasive, prohibited noxious weed in Minnesota. It can form dense mats several feet deep covering and inhibiting the growth of all other vegetation. It is relatively new in the state. The first recorded sighting was in 1992. To date, it has been reported in just four counties in the southeastern corner of the state, and in Hennepin and Scott Counties in the metro area.
Japanese hop closely resembles the native common hop (Humulus lupulus). Japanese hop is distinguished by the leaf stalk that is as long or longer than the blade; the leaf blade that has 5, 7, or 9 lobes and is rough to the touch on the underside; the stiff hairs on the margins of the bracts on the fruiting structure; and the lack of stalked, yellowish glands on the fruiting bracts, anthers, and seed capsules. Also, unlike common hop, the fruiting structure is not fragrant when crushed, and it cannot be used for making beer.
Brownsville Bluff Scientific and Natural Area, in Houston County, was designated on January 19, 2016, to protect habitat for the milk snake and the state threatened western ratsnake. Neither snake is poisonous. The site consists of 286 acres bedrock bluff covered with windblown sediment. The 39-acre south section is a wildlife sanctuary that is closed to the public. The eastern-facing slopes are moderately steep to very steep. They have a mature, moderately moist forest of sugar maple, basswood, ironwood, northern red oak, and white oak. The west-facing slopes are less steep. They have a dry to moderately moist mature forest of bur oak, northern pin oak, northern red oak, and paper birch, with some shagbark hickory, white oak, and black walnut. At the top of the bluff there is a prairie that has been used as an agricultural field. It will be restored to prairie and savanna.
An access road leads from the parking area (walk around the gate) 0.67 miles to the top of the bluff. A footpath follows the cleared fields on the bluff top to the northern boundary. Another footpath leads east from there to a spectacular overlook at the northeast corner of the SNA, a dizzying 400 feet above the road below.
Designated on June 12, 2017, Lawrence Creek SNA is one of the newest Scientific and Natural Areas in the Minnesota DNR’s inventory. It consists of 71.8 forested acres of steep bluffs and deep ravines near Franconia in Chisago County. Included within its boundary is a trout stream, a hunting shack, and an 11-acre state wildlife sanctuary. The sanctuary is closed to the public and visitors are asked to “Stay back from cliffs and off steep slopes” to protect sensitive plant communities. There are no maintained trails, but there is a forest road and worn footpaths that together complete a 3.2-mile circuit of the site.
Visitors to Lawrence Creek SNA this week (May 6 to 12, 2018) will see Pennsylvania sedge in flower and sharp-lobed hepatica and yellow marsh marigold peaking. Other spring wildflowers in bloom this week include bloodroot, white trout lily, large-flowered bellwort, large-flowered trillium, and Virginia spring beauty. Louisiana Waterthrush, a species of special concern, has been heard here. The site contains habitat that may host Cerulean Warbler, Acadian flycatcher, and Red-shouldered Hawk. Three Helmeted Guineafowl were seen in the parking area by a surprised visitor. They apparently belong to the farm across the road and are free to roam the adjacent fields.
Checkered white (Pontia protodice) is a medium-sized butterfly with a wingspan of 1½″ to 2½″. It is a southerly species and is uncommon in Minnesota. There are two overlapping broods here, early June to August (spring form) and July to mid-October (summer form). The wings are white with dark markings, including a checkered pattern on the outer margin. The female has more extensive markings than the male, and the spring form has darker markings than the summer form. The larva (caterpillar), known as the southern cabbageworm.
Checkered white populations have drastically decreased in eastern Unites States, and the butterfly is now scarce or extirpated in some areas where it was once common. It appears stable in the west. The cause of the decline is unknown, though habitat loss is certainly a contributor. It is possible that the extremely abundant introduced species cabbage white is displacing native whites, including checkered white. It is also possible that checkered white is a western and midwestern species that only sporadically became abundant in eastern agricultural fields. It remains to be seen whether the decline will continue to spread westward.
Pst on Canada thistle
Visitors to Minnesota’s natural places will occasionally come across a stand of Canada thistle with a few plants that are whitened at the top, appearing bleached. The discoloration is caused by the bacterium Pseudomonas syringae pv. tagetis. It has been called “White‐colour Disease of Canadian Thistle,” “apical chlorosis of Canada thistle,” and “Bacterial Speck”, but it has no widely-accepted common name. It is often referred to in scientific literature as Pst.
Outside of a laboratory, a bacterium is recognized only by the symptoms it produces in its host. Pst produces the substance tagetitoxin, which blocks the production of chloroplasts, preventing photosynthesis. This results in whitened plant growth (chlorosis) on only the upper portion of the plant, stunted growth, fewer shoots, and inhibition of flowering. Pst infects plants in the Aster family, including Canada thistle, common dandelion, common sunflower, common ragweed, giant ragweed, Jerusalem artichoke, and some other plants not found in Minnesota.
Researchers at the University of Minnesota conducted a study in 2002 to assess the viability of using Pst as a biological control agent for Canada thistle.