Caterpillar & BTK FAQ
Alberta Tent Caterpillar Outbreak 2026 – BTK FAQ
Alberta is currently experiencing a widespread forest tent caterpillar outbreak. While the number of caterpillars can be alarming, most healthy deciduous trees can recover after a single season of defoliation. BTK is one of the safest and most targeted options for reducing caterpillar feeding damage.
What is BTK?
BTK, or Bacillus thuringiensis var. kurstaki, is a naturally occurring soil bacterium used to control caterpillars. It is commonly used for tent caterpillars, cabbage worms, loopers, and other moth and butterfly larvae.
Does BTK kill tent caterpillars?
Yes. BTK is effective against young tent caterpillars when they actively feed on treated leaves. After eating BTK, the caterpillar stops feeding and dies over the next few days.
Does BTK work on Alberta forest tent caterpillars?
Yes. Forest tent caterpillars are one of the main pests BTK is used for. Timing matters: BTK works best when caterpillars are small and actively feeding.
How quickly does BTK work?
BTK is not instant. Caterpillars usually stop feeding within 24–48 hours, then begin dying within 2–5 days. You may still see live caterpillars for several days after spraying.
Does BTK kill on contact?
No. BTK must be eaten. Spraying it directly on a caterpillar will not usually kill it unless the caterpillar later consumes treated foliage or residue.
Will BTK work if caterpillars are hiding inside webs?
Partially. BTK only works where it reaches the feeding surface. Caterpillars protected inside dense webbing may avoid exposure until they leave to feed.
For heavy infestations, break open webbing where practical, spray the surrounding foliage thoroughly, and reapply according to the product label if feeding continues.
Does BTK kill beneficial insects?
BTK is highly selective. It mainly affects caterpillars and does not generally harm ladybugs, lacewings, predatory mites, bees, predatory beetles, or earthworms.
However, BTK can affect desirable butterfly and moth caterpillars if they eat treated foliage.
Does BTK kill spider mites?
No. Spider mites are arachnids, not caterpillars. For spider mites, use appropriate mite controls or predatory mites such as Phytoseiulus persimilis or Neoseiulus californicus.
Does BTK kill aphids?
No. BTK only controls caterpillars.
Does BTK kill wireworms?
No. Wireworms are beetle larvae and are not controlled by BTK.
When is the best time to spray BTK?
Apply BTK in the early morning or evening when caterpillars are actively feeding. Evening applications are often preferred because sunlight gradually breaks BTK down.
How often should BTK be applied?
For active infestations, reapply every 7–10 days if caterpillars remain active, or after significant rainfall. Always follow the directions on your specific product label.
Can BTK save a tree that has already been defoliated?
BTK prevents further feeding damage, but it cannot replace leaves that have already been eaten. Healthy deciduous trees often recover and may produce a second flush of leaves after caterpillar feeding.
Why are there so many tent caterpillars this year?
Tent caterpillars naturally go through boom-and-bust population cycles. Outbreaks can last several years before collapsing due to weather, disease, predators, and parasites.
Should I spray every tree on my property?
Not always. Treatment is most useful for young trees, newly planted trees, heavily stressed trees, severe defoliation, or caterpillars causing nuisance problems around homes, patios, sidewalks, or businesses.
Large, mature, healthy trees can often tolerate one season of feeding and recover naturally.
Is BTK organic?
Many BTK products are approved for organic gardening because the active ingredient is a naturally occurring bacterium. Check the specific product label if organic certification matters.
Bottom line
If you are dealing with Alberta’s current tent caterpillar outbreak, BTK is one of the safest and most targeted control options available. Apply it early, spray foliage thoroughly, and remember: BTK must be eaten to work.
About Caterpillars
Caterpillars are a huge problem in Canada. They can defoliate trees and destroy your garden in a matter of days. Even though you may not see the caterpillars themselves, evidence can be found in the form of droppings and foliar damage.
Cabbage worms are green and like to hide on the underside of leaves. They especially like to prey on leafy greens like lettuce, kale and cabbage, and have been known to destroy young cauliflower plants before they have a chance to flower. It is important that you identify a cabbage worm infestation immediately.
There are two main varieties of tent caterpillar currently found in Alberta:
Forest tent caterpillars, the blue variety of tent caterpillar, defoliated 4.8 million hectares of Canadian forest in 2015.
If you find an actual tent in a tree, that tent is most likely to belong to the Eastern tent caterpillar, which are black and orange. These caterpillars cause less damage than the forest tent caterpillar, but are unsightly.
LDD Moth Caterpillars (Lymantria dispar dispar, "European Gypsy Moth") are often confused with tent caterpillars. They are considered an invasive species and a very serious pest and steps should be taken to eliminate them as soon as they're spotted.
Safer's BTK Caterpillar Killer is a biological insecticide that controls caterpillars including cabbage worm, tomato hornworm, tent caterpillars, LDD moth, leafrollers, and other listed insects. Simply mix the concentrate with water and spray on vegetables, fruit, trees, and ornamentals. After ingesting the treated portion of the leaf, caterpillars stop feeding within hours and die within a few days. This 100mL concentrate makes 33.3L of solution.
- Controls caterpillars including cabbage worm, tomato hornworm, tent caterpillars, LDD moth, leafrollers, and other listed insects
- Can be used on vegetables, fruit, trees, and ornamentals
- Active Ingredient: Bacillus thuringiensis subsp. kurstaki, strain ABTS-51
- Makes 33.3L
- BTK is generally regarded as environmentally safe, as its toxicity is essentially limited to its target pest; humans, wildlife, and beneficial insects are regarded as unaffected by the pesticide. This means that you'll only be killing pesky caterpillars, not your bee friends!
Cabbage Loopers
Identification: These bright green or turquoise inchworm-like caterpillars are typically found on the undersides of your leaves. They are well camouflaged. Leaves may appear weighted-down.
Control: Pyrethrins, insecticidal soap, yellow sticky traps, diatomaceous earth, hand-picking.
Biological Control: BTK
Notes: Caterpillars are typically only a problem on outdoor grows. They must be dealt with swiftly, as they can devour your entire crop in a matter of days. Plants such as lettuce, Swiss chard, cabbage and cauliflower are magnets for cabbage loopers. Kill any moths that enter your grow room.
LDD Moth Caterpillars
Identification:
Control: Pyrethrins, insecticidal soap, burlap, sticky traps, duct tape wrapped "sticky side" out around the base of your trees, folded burlap cloth wrapped around trees, hand-picking, water jets, stomp.
Biological Control: BTK
Notes: The LDD Moth is an invasive species that puts Canadian forests at risk. These caterpillars can defoliate your decorative trees extremely quickly, and thus must be dealt with immediately. They are covered in small hairs that can cause rashes in susceptible people. We recommend you use gloves when handling them.
To treat a caterpillar exposure:
SOURCE: https://www.poison.org/articles/caterpillar-stings
- If the caterpillar is on the skin, remove it without using your hands!
- Gently put tape over the exposed area, sticky side down. (Any kind of tape will do.)
- Pull up the tape, removing the hairs or spines.
- Repeat with fresh pieces of tape as often as needed to treat the area involved.
- Wash the area gently with soap and water.
- If the area itches, put on a paste of baking soda and water.
- If that doesn't help, try a hydrocortisone cream.
- If that doesn't help, try an antihistamine cream. That shouldn’t be the first choice, as it doesn't always help. Also, some people have skin reactions to these creams.
- If the area is badly blistered, contact your health provider.
- Call your health provider about a tetanus booster if your shots are not up to date.