If your water lily leaves look like someone took a hole-punch to them… congrats (sorry) — you may have China Mark Moth caterpillars. They’re tiny, sneaky, and weirdly good at making “leaf boats.” 🙃

Water Lily Pests: How to identify and treat China Mark Moth caterpillars without harming fish in my water garden

China Mark Moth caterpillars are common water lily pests that cut “shot holes” in water lily leaves and hide inside little floating leaf cases (“leaf boats”). The most fish-safe approach is to remove and destroy the leaf boats and damaged leaves, then (if needed) use a targeted caterpillar treatment like Bacillus thuringiensis kurstaki (Bt-k) on the foliage, following the label.

What are China Mark Moth caterpillars?

The China mark moth in U.S. water gardens is commonly Nymphuliella daeckealis. Adult females lay eggs near the leaf edge or underside, and the larvae do the damage.

Why they’re so annoying:
They cut pieces of water lily leaf and use them like a protective “case” so they can float from plant to plant.

What does China Mark Moth damage look like on water lilies?

Look for these classic signs:

1. Tiny “shot holes” on leaf edges (often early damage).

2. Bigger cutouts missing from the leaf edge as larvae grow.

3. Leaf skeletonizing (leaf turns into lace).

4. Floating “leaf boats” / leaf sandwiches (two leaf pieces held with silk).

5. Leaves stuck together, or larvae boring into the leaf stem (petiole) which can kill whole leaves.

When do China Mark Moth caterpillars show up?

They’re often worst mid-summer through early fall in many areas. In Maryland research, adults were common from mid-July to late September with overlapping generations. Mark Moths and caterpillars are found across the USA anywhere you find water and water plants, in parts of the southeast where there is a lot of water they can be close by and you may have to treat a few times a year from nearby water ways. 

Fish-safe “Do This First” plan (no chemicals)

This is the #1 best answer for a fish pond.

Step-by-step

1. Scan your water lilies for leaf boats and fresh holes.

2. Remove and destroy any leaves/stems with larvae attached.

3. Net out the floating leaf boats (don’t let them drift to the next lily).

4. Flip boats open and remove the larva. Fun fact: University of Maryland observed that if you pull larvae out of their leaf case and put them in the water, they sink and die—the case is critical for their survival.

5. Repeat weekly during the peak season until you stop seeing new boats.

Good news: University of Maryland notes mechanical removal alone can reduce larval numbers to acceptable levels in some ponds.

If I still have them… what’s the safest treatment around fish?

Bt-k (Bacillus thuringiensis kurstaki) is the “targeted caterpillar” option

University of Maryland trials found the microbial insecticide Bt kurstaki strain effective on China mark moth larvae.

Why pond owners like Bt products:

• Bt-k targets leaf-feeding caterpillars specifically.

• Compared to many common insecticides, Bt products are described as nontoxic to people, pets, wildlife, and organisms not closely related to the target pest.

• Bt must be eaten to work, and sunlight breaks it down, so you may need repeat applications. Rain will wash it off as will a garden hose and negate the effect. 

How to use Bt-k on water lilies (fish-safe habits)

1. Choose a Bt product labeled for caterpillars (look for kurstaki on the label).

2. Spray the water lily leaves, focusing on the damaged areas when it will not be raining. 

3. Avoid spraying directly into the pond water as much as possible, it wont harm anything but is a waste of the product and can kill larvae of other beneficial insects.

4. Re-apply as needed (Bt breaks down fast in sunlight and washes off in rain). 

Important “keep fish safe” note: Bt itself is usually the safer part — but store products include other ingredients that can carry more risk, so always follow the label.

What about spinosad?

University of Maryland also found spinosad effective in trials.
But for a fish water garden, use extra caution: only use products labeled for aquatic settings and follow directions exactly.

Extra-safe approach (if your lilies are in pots): UMD notes that when lilies are in pots, you can pull them out, let foliage dry, treat, let dry again, then return the pots to the pond.

What should I NOT do in a pond with fish?

Because we like fish alive and well:

• Don’t use random “yard insect killers” that are not labeled for aquatic use. (EPA has limited aquatic-labeled options because pesticides can move into waterways.)

• Don’t assume “natural” equals “safe for fish.” Always read the label.

Product connection (simple, helpful, not pushy)

If you want to tie this article back to Pond Megastore solutions without getting weird about it:

• Pond Nets (to scoop leaf boats fast)

• [Pond Gloves / Long Arm Gloves (because leaf boats are gross, and you deserve dignity)

• Water Lily Fertilizer Tablets (healthy water lilies recover faster after pest damage)

Key Takeaways (quick summary)

• China Mark Moth caterpillars make shot holes and floating leaf boats on water lilies.

• The most fish-safe control is mechanical removal: remove damaged leaves and scoop out leaf boats.

• Bt-k (Bacillus thuringiensis kurstaki) is a targeted caterpillar treatment shown effective in trials and is widely viewed as safer than many broad insecticides when used correctly.

• Apply any treatment to foliage, minimize overspray into the water, and follow the label every time. - remember rain will was this off and negate the treatment as would a garden hose.