Invasive Species

An invasive species are plants, animals and micro-organisms introduced by human action outside of their natural past or present distribution whose introduction threatens the environment, economy or society, including human health (Government of Canada, 2004).

There is a growing list of invasive species infiltrating Bobs and Crow lakes, and pose the largest natural threat to the long term health of the lakes.   For an in-depth discussion of invasive species go to:

Aquatic Invasive Plants

Eurasian Milfoil prefers water 1-3 m deep. Tiny plant pieces can develop into new plants.

Invasive plants are by far the most distressing threat to cottage owners and guests.  They affect boating, swimming, fishing and other recreational activities.  Residents and guests are increasingly frustrated with the "weedy" water fronts.   Care should be taken when trying to cut or remove these plants as they can easily spread from cuttings that re-root elsewhere on your lake front.   Common species are Eurasian Milfoil, European water chestnut,  fanwort, hydrilla, and water hyacinth.


Dime-sized Zebra Mussels

Invasive invertebrates include mussels, crayfish, snails, clams and waterfleas.   They adversely impact our aquatic ecosystems by out-competing for food and habitat with native fish species, and destroying fish spawning habitats.

Until very recently, there were no confirmed sightings of zebra mussels in Crow and Bobs lakes.   Unfortunately their presence in both lakes has now been reported by several residents.   It is hoped that their spreading within the lake will be constrained by the high calcium content of the water, which inhibits the growth of the shells of zebra mussels.  

This websiste offers an informative summary and a Zebra Mussels primer on the topic.

Zebra Mussels 101 

Invasive Fish

Black Crappie populations are increasing in Bobs Lake.

Although Bobs and Crow lakes do not have any of the severe predator species such as Asian Carp and Round Goby, there has been an introduction of other native species from other lakes.   The most notable is the Black Crappie.

Black Crappie while a good eating fish preys on young walleye.  Walleye (or pickerel) is a very popular fish among avid sports fishing enthusiasts on Bobs and Crow lakes. Many local fishermen feel the Black Crappie has contributed to reduced walleye catches in recent years.


Invasive Plants

Parsnip sap can cause severe skin burns.

Invasive plants that crowd out native species are a major objective of educational programs, to teach residents that what appears to be an attractive flowering plant is not necessarily good for the natural environment of the lakes.   Some of the most common invasive species are shown below:

Wild Parsnip is a member of the carrot family, whose sap contains chemicals that cause human skin to react to sunlight, resulting in intense burns, rashes or blisters.  Protective clothing and care should be exercised when gathering this plant.

Hogweed sap can cause severe inflammation of the skin.

Giant Hogweed is also a member of the carrot family. 

The stems of the plant are covered with reddish-purple flecks and stiff hairs filled with sap.   

Severe burns can result from this sap getting on the skin which is then exposed to sunlight.   Symptoms occur within 48 hours and consist of painful blisters.   

Forest Pests

Tent caterpillars are the largest defoliator of hardwood trees in N. America.

The Tent Caterpillar is native to North America and is not an invasive species.  However residents of Bobs and Crow lakes experienced a severe outbreak of the caterpillars in 2018.   Periodic outbreaks occur every 10-12 years and typically last from 3 to 6 years in a particular area.

Lymantria Dispar Dispar (LDD): The Moth Formerly Known as Gypsy*

During 2021 the Lymantria Dispar Dispar (LDD) larvae decimated many of the trees around Bobs and Crow Lakes. They prefer oak and other hardwood such as maple or basswood, but they will eat most trees, including coniferous. The Ministry of Northern Development, Mines, Natural Resources and Forestry (MNRF) monitors LDD defoliation and provides a forecast for the following season. In 2020, based on their observation, they predicted that 2021 would be bad. They were not wrong! Barring a population collapse over the coming winter, the forecast for 2022 doesn’t look good. A healthy tree can survive a year of heavy LDD moth infestation. Deciduous trees can re-foliate later in the summer. Conifers cannot. Successive years of LDD infestation kills trees. Trees already weakened and stressed from drought, pollution, construction, previous infestations of LDD or other pests cannot survive.

The damage is done to the tree during the larvae stage.

Newly Hatched LDD Larvae-Caterpillars.

The caterpillars emerge in mid-April to mid-May from egg sacs. Mid-May to mid-June sees the heaviest damage to trees as the caterpillars mature. Caterpillars are 5 to 60 mm long and covered in hairs. They climb into the canopy and eat. In the 40 days they spend growing, munching, and moulting, each one can chew through a square meter of foliage. For two weeks in mid-June through July the caterpillars cocoon. Adult moths emerge in late July and August to lay their eggs. Adult moths only live for about 10 days, and do not feed. The eggs masses are 4 cm long, tan in colour, and contain up to 1000 eggs. Female moths are white, small, and flightless, whereas the beige males are larger and fly. The egg sacs overwinter, and the cycle begins again the following spring.

LDD are an invasive species. Accidentally introduced in the 1860s, there have been periodic outbreaks since, often in 7-to-10-year cycles, usually ending in an overabundance and a population collapse. That hasn’t happened yet, and this outbreak shows no signs of abating. Climate change has disturbed some natural controls of LDD. Several successive days of winter temperatures below minus 20 Celsius will kill a substantial number of the egg masses.

LDD Caterpillar (Larvae)

We have not had this level or duration of cold over the last several years. The Nuclear Polyhydrosis Virus (NPV) disrupts the eating habits of the caterpillars, then converts the inside of the caterpillar to millions of virus particles, which helps to propagate the virus. Unfortunately, drought kills this virus. We have had a couple of summers with periods of extreme drought. The fungus Entomophaga Miamaiga exists as resting spores on tree bark throughout the winter, germinating into sticky spores in the spring. This fungus then digests its way into the caterpillar on contact, killing the caterpillar and turning the decomposing carcass into microscopic spores that spread. Unfortunately, this fungus relies on specific moisture levels and temperatures in order to germinate. The conditions required to ensure a collapse of the LDD population are not occurring.

Parasitoids refer to species of wasps and flies that lay their eggs in the body of a host, such as LDD caterpillar. The larvae stage of these parasitoids kill the host. One parasitical wasp Ooencyrtus kuvanae has been introduced into the US to help control LDD. Four generations of this wasp can occur in a year. Another specialised wasp introduced into the US specifically to control LDD moth is the Cotesia melanoscelus, and a fly called Compsilura coccinnata. Some insects such as Calosoma beetle feeds almost exclusively on LDD moth caterpillars. It has been introduced into north-eastern US, and the great lakes area as a long-term solution to the LDD moth.

There are a few things you can do. Egg masses are laid in August.

LDD Egg Masses.

Throughout the fall, winter, and spring you can scrape off the egg masses. Once hatched, the caterpillars climb up and down the trees. You can put burlap bands around the trunk of the tree. The caterpillars will gather under the burlap. Collect and dispose of them. Destroy the pupae when you find them. Do not put duct tape on trees, as beneficial insects and birds get caught. Traps to attract male moths aren’t very effective because of the sheer number of both female and male moths.

Male & Female LDD Moths.

Some native insects are good predators such as predatory stinkbugs, many ants, and spiders. In this part of the world, spiders are very beneficial. These insects and parasitic wasps and flies are harmless to people. Throughout the year you can encourage insects such as parasitic wasps and birds that feed on eggs, caterpillars, and pupae. LDD caterpillars are hairy and not the favourite snack of many birds, but blue jays, orioles, black-billed and yellow-billed cuckoos, and rufous-sided towhees will all eat LDD caterpillars. Chickadees will eat the egg masses. Bio-diversity is always a good goal when looking to help mitigate an outbreak of anything. Aim to build a habitat that will attract birds and beneficial insects. Check out for help making your garden friendly to all sorts of insect and caterpillar-loving birds! Ninety six percent of terrestrial birds rear their young on insects, including caterpillars.

Some residents on the lake have had success with Bt-k. Bacillus Thuringiensis, subspecies Kurstaki (Bt-k) is a natural soil-borne bacteria that can be sprayed onto the leaves. Bt-k produces a protein crystal during the spore-forming stage of its life cycle, which is toxic only to the larvae stage (caterpillar) of lepidoptera. These microscopic crystals are ingested by caterpillars feeding on treated leaves. In the alkaline environment of the targeted insect’s digestive system, the crystals are converted into toxic protein molecules that destroy the walls of the insect’s stomach. The insect stops eating within hours and is dead in 2 to 5 days. It must be ingested by the feeding caterpillars, so it must be sprayed in the spring. Bt-k washes off the leaves so timing is very important. It is usually done in two applications. Bt-k kills only lepidopteran larvae that are feeding at the time it is sprayed. LDD caterpillars feed earlier than monarchs and swallowtails who feed exclusively on milkweed and plants of the carrot family later in the summer. In Canada there are approximately 5400 species of Lepidoptera in 81 families. Bt-k kills any Lepidoptera larvae that are feeding at the time of spraying.

BT-k is best applied aerially, usually by helicopter, and usually in two applications 7 to 10 days apart. Zimmer Air Services is the company that sprayed for some residents around the lake in 2021. Each resident requires an individual contract with Zimmer Air for spraying. Their website has lots of information. Or call: 1 800 665 5484, or 1 888 840 4830. Or email In 2020 the cost was approximately $360 for the first acre, plus $96 for each additional acre.

*In July 2021 the Entomological Society of America removed “gypsy moth” as a recognised common name from their “Common Names of Insects and Related Organisms List.” This was part of their program to review and replace insect common names that may be inappropriate or offensive because they perpetuate negative ethnic or racial stereotypes. Lymantria Dispar Dispar is a mouthful, so LDD Moth is its new common name.

Reporting Sightings

Reporting new sightings on Bobs and Crow lakes of an infestation of an invasive species potentially can help with their control.   For extensive information on invasive species, go to