What Eats Canada Thistle?

What eats Canada thistle? Four species of insects – two weevils, a fly, and a beetle – are known to feed off of the troublesome, aggressive weed species known as the Canada Thistle.

The four insects that are typically used for Canada thistle removal are examined in brief detail below.

 The Canada Thistle Stem Weevil

• This insect literally “mines” holes into the plant.
• The weevil larvae dig into the stem, weakening the thistle and leaving it open for other pathogens to make their way in.
• The weevil itself won’t kill the plant, but it weakens it sufficiently so that other relatively non-destructive methods will make quick work of doing so.

The Canada Thistle Bud Weevil

• These weevil weaken the plant by attacking the flowering buds, burrowing in and removing producing seeds, stunting the plant and cutting down on growth in the area.

• These weevil burrow into the stems and shoots of the plant, and weaken it much like the stem weevils.
• Their attacks are centered on the bud of the plant rather than the stem, however.
• In this case, the weevil is doing the damage and other pathogens aren’t necessary to kill off the plant.

The Thistle Stem Gall Fly

• These flies burrow into the stems and shoots of the plant, and weaken it much like the stem weevils.
• Their attacks are centered on the bud of the plant rather than the stem, however.
• In this case, the weevil is doing the damage and other pathogens aren’t necessary to kill off the plant.

The Defoliating Beetle

• The beetle chews into the leaves and stems of the plant.
• It doesn’t typically kill it but can cause substantial weaknesses.

Canada Thistle

So, why is it important to know what eats Canada Thistle?

• The Canada Thistle is listed as a noxious weed across the United States (and Canada) and is considered one of the most invasive, troublesome species for farmers.
• The thistle is directly responsible for millions of dollars lost every year, both in destroyed crops and in expensive attempts to kill it and remove it.
• The Canada Thistle is distinguished by very long running roots, which tangle shallowly beneath the soil.
• The plant itself opens into a slim purple flower.
• The thistle thrives everywhere from road sides to pastures.
• It is particularly invasive in farmlands because cattle will not graze near it, thus allowing it free reign of the area.
• Considering the expense of controlling it, it’s little wonder that farmers and agriculturalists have looked to simple, biological solutions such as the insects listed above.
• Once it was determined that these insects, by their natural eating habits, help control the thistle’s domination of a given area, the insects have been deliberately moved to those areas, where they have for the most part now become native species.
• When and if the use of the insects is successful, it’s a victory in multiple ways: not only is it cheaper than mechanical or chemical methods of thistle removal, but it’s also much simpler and ultimately much less damaging to the surrounding environment.

So, now you know what eats Canada Thistle and why those insects are used to control it.