Trap Guide

DIY CIRCLETRAP GUIDE

Circle traps are the most effective mechanical tool for capturing spotted lanternfly without harming birds, butterflies, or other wildlife. Here's how to build and install them using the free Penn State Extension design.

Cost: $2–5 per trap. No chemicals, no glue, no bycatch. A single trap on a productive Tree of Heaven can capture thousands of SLF per season.

How Circle Traps Work

Circle traps — also called funnel traps or bark band traps — exploit a simple SLF behavior: they climb tree trunks in huge numbers.

The Basic Principle

A circle trap wraps around a tree trunk like a collar. The bottom is open, allowing climbing SLF to enter. Inside, a funnel of window screen mesh directs them upward into a collection bag at the top. Once inside the bag, they can't navigate back out.

The collection bag typically contains soapy water, which kills trapped insects. The entire device is passive — no power, no chemicals, no monitoring required between checks.

Penn State Extension developed and tested the original design, which is available free at their extension website. Their research showed catch rates of up to 200 SLF per day on high-traffic trees during peak adult season.

Seasonal Timing

June

Early nymphs begin climbing — good time to install traps before peak season.

July

Later nymph instars climbing heavily. Traps start catching significant numbers.

August

Adults emerging and climbing. Peak trap activity begins.

September

Highest catch rates of the season. Check traps every 2–3 days.

October

Adults continue through October. Egg-laying begins. Traps still highly effective.

November

Activity slows with cooler temperatures. Remove traps for storage by late November.

Why Circle Traps Beat Sticky Bands

Sticky tape bands were the original recommendation — but they have serious problems that circle traps avoid entirely.

No Bird or Butterfly Bycatch

Sticky bands trap songbirds, butterflies, and other beneficial insects that get stuck on the adhesive. Circle traps work mechanically — insects walk up into a funnel they cannot escape, but birds and larger animals are not affected.

Species-Selective by Design

The design exploits SLF behavior specifically: they climb tree trunks in large numbers. Most other insects that share this habitat are smaller or fly rather than climb, reducing incidental capture significantly.

No Glue Mess or Residue

Sticky bands leave adhesive residue on tree bark and require careful disposal. Circle traps are reusable season after season with no chemical residue. The mesh can be cleaned and stored between seasons.

High Capture Volume

Well-sited circle traps on high-traffic trees can capture 50–200 SLF per day during peak adult climbing season (late August through October). A single trap on a productive Tree of Heaven can yield thousands per season.

Combining Both Methods

Sticky bands still have a role: as monitoring tools. A small sticky band low on the trunk tells you whether SLF are present and how many. Use sticky bands to confirm SLF activity, then install circle traps above them for the actual capture work. Remove sticky bands once circle traps are in place to eliminate bycatch risk.

Materials Needed

All materials are available at hardware stores. Total cost per trap: $2–5 for DIY builds.

Window screen mesh

Fiberglass or aluminum, approximately 18 inches wide. Needed to form the cone funnel. Hardware stores carry it by the roll.

Hardware cloth (optional)

1/4-inch mesh hardware cloth can reinforce the structure on rough-barked trees and helps the funnel hold its shape in wind.

Staple gun and heavy-duty staples

For securing mesh to tree bark. Use staples long enough to penetrate bark but not damage living wood — 5/16 inch or 3/8 inch typically works.

Wire or zip ties

For closing the seam and adjusting fit around the trunk. Zip ties are fast to install; wire is more durable long-term.

Collection bag or jar

The Penn State design uses a 1-quart plastic bag. Fill with a small amount of soapy water to kill captured insects. Replace when full or every 2–3 days.

Step-by-Step Installation

Each trap takes 20–30 minutes to install. Once installed, it works passively until you empty it.

Choose your target tree

Tree of Heaven is your #1 priority — it's the primary SLF host and will attract the most insects. Then target smooth-barked trees: black cherry, silver maple, big-leaf maple, willows. Rough-barked old oaks are lower priority.

Clear the area around the trunk

Remove any vines, dead bark, or debris from the trunk at the installation height. The mesh needs to sit flush against bark — any gaps allow SLF to bypass the trap.

Wrap and shape the mesh

Wrap the window screen around the trunk at 4–5 feet, forming a cone or funnel that angles upward. The wide end faces down (open to climbing insects), the narrow end at the top feeds into the collection bag.

Staple securely with no gaps

Staple the mesh to the bark around the full circumference at the bottom, top, and seam. Run your hand around all edges — any gap larger than 1/4 inch is a potential bypass route.

Attach the collection bag

Tie or wire the collection bag opening tightly to the top of the funnel. Add 2–3 tablespoons of dish soap and 1/2 cup of water. The soapy water kills insects that fall in.

Checking and Emptying Your Trap

Traps require minimal maintenance — but regular checking keeps them performing and tells you how bad SLF pressure is on your property.

Check Every 2–3 Days

During peak season (August–October), check traps every 2–3 days. A full bag can make the trap less effective and attracts predators. During the early season (June–July), once a week may be sufficient.

What You'll Find

Mostly SLF at various life stages — nymphs in early summer, adults from late July onward. You may also find a small number of other insects. This is normal and far fewer non-targets than sticky bands would catch.

What Counts as a Good Catch

Any catch is valuable. A trap that catches 10–30 per day is performing well. Traps on prime TOH trees with established SLF pressure often catch 100+ per day at peak. If your trap is catching nothing after 2 weeks, check for bypass gaps.

Disposal

Empty the collection bag into a container of soapy water, then dispose of the contents in a sealed bag in the trash. Do not compost or pour live insects onto the ground — SLF can survive water immersion for short periods.

DIY vs. Commercial Options

Both work. The choice comes down to time versus cost.

DIY Penn State Design

Free plans from Penn State Extension. Total cost $2–5 per trap in materials. Requires about 20–30 minutes to cut and install. Highly effective when built carefully. Can be made from materials at any hardware store.

Commercial Circle Traps

Several companies now produce commercial circle traps based on the Penn State design. These run $15–40 per trap but come pre-cut and include instructions. Worth it for large-property applications where time is at a premium.

Recommendation: Start with 1–2 DIY traps on your highest-traffic trees to confirm performance in your specific situation. If catch rates are high, expand with additional DIY or commercial traps. Penn State Extension plans are free — search “Penn State circle trap SLF” for the latest design specifications.

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