The Biggest Threats and How You Can Help
The Hawaiian Islands’ natural beauty hide a constant battle against invasive species. From Maui forests to beaches to farmlands, invaders have altered ecosystems, threatened endangered species, and cost farmers and taxpayers millions.
Here’s a closer look at some of the most destructive invasive species on Maui, their history, impacts, and what we do to fight back.
Axis Deer (Axis axis)
Brought to Maui in 1959-60 as a game animal, axis deer have multiplied into herds estimated in the tens of thousands today (some say they could be up to 100,000 by now!) With no predators, populations grow by about 20% each year.
Deer devour crops, strip native vegetation, and leave hillsides bare, which worsens erosion and mudslides into streams and reefs. Farmers have reported losses of tens of thousands of dollars in a single season. They also pose a safety hazard, police logged 173 deer-vehicle collisions in 2021, more than double just three years earlier. We’ve personally almost hit them dozens of times (and I hit one once. It was ok, since I was driving slowly, but my hood wasn’t!)
What’s being done: Maui County declared a state of emergency in 2021, forming an Axis Deer Task Force. There’s year-round hunting of axis deer on Maui with no bag limits, deer-proof fencing around farms, and meat-harvest programs like Maui Nui Venison that turn culls into food and profit. Officials estimate 12,000 deer still need to be removed to bring populations down to a sustainable level. Some places like the Makawao General Store have fridge cache’s for hunters with too much meat, available for locals to grab.
How to help:
- Report injured or dangerous deer to DOFAW Maui (808-984-8100) or DOCARE (808-873-3990).
- Support management programs, allow hunters access to private land, or get a hunting license through DLNR (with proper weapons training, safety protocals, and permission to hunt on the land you’re on.)
Feral Pigs (Sus scrofa)
First introduced by Polynesians and later Europeans, feral pigs now roam Maui’s forests, farms, and even residential areas. Are they sus? Without doubt. We once almost got taken out in a ravine by a big one that came out of nowhere!
Their rooting destroys native plants, spreads invasive weeds, and creates muddy wallows that breed mosquitoes, a direct driver of avian malaria, which is devastating native forest bird populations. They also damage crops, cause erosion, and spread diseases like leptospirosis (don’t drink stream water!)
What’s being done: Public hunting is open year-round in designated areas, and conservation agencies like Haleakalā National Park and the East Maui Watershed Partnership fence critical areas and remove pigs inside. Fencing projects have shown dramatic forest recovery once pigs are eliminated.
How to help:
- Allow hunters access to affected lands.
- Join volunteer fence maintenance and removal trips with watershed partnerships.
- Report new incursions to 643-PEST.
- Make sure to keep your distance, as they can be dangerous when they feel threatened.
Little Fire Ant (Wasmannia auropunctata)
Tiny but devastating, little fire ants (LFA) arrived on Maui in 2009. They form supercolonies, swarm over people, pets, and wildlife, and deliver painful stings that can cause blindness in animals.
Maui has detected 25 infestations so far, and 10 sites remain under treatment. Vigilance has kept them from spreading island-wide, unlike Hawaiʻi Island where LFAs are entrenched!
What’s being done: MISC and the Hawaiʻi Ant Lab are aggressively treating sites with specialized baits, sometimes even by helicopter. Community reports have been critical with 72% of detections coming from residents who noticed stings and called it in.
How to help:
- Test your yard with a peanut butter stick and send samples in.
- Report suspected ants to 643-PEST or MISC (808-573-6472).
- Learn more at StopTheAnt.org
Coqui Frog (Eleutherodactylus coqui)
Accidentally introduced from Puerto Rico in the late 1980s, the coqui frog’s piercing “ko-kee” call reaches 80–90 decibels, as loud as a car alarm. Some people hate it, some people love it, but regardless of whether you like their sounds, they’re destructive.
On Maui, coquis are mostly confined to a six-square-mile zone in Haʻikū, thanks to relentless spraying and community control. Left unchecked, they could spread like on Hawaiʻi Island, where forests now echo with millions of frogs nightly. Ecologically, coquis devour insects by the hundreds of thousands, disrupting native food webs.
What’s being done: MISC crews spray citric acid, and community groups receive free supplies and training to keep their yards frog-free. Outlying populations have been eradicated before they could spread.
How to help:
- Report any coqui calls outside Haʻikū to 643-PEST or MISC (808-573-6472).
- Pick up free citric acid from MISC to treat your yard.
- Volunteer with local neighborhood spray teams.
Miconia (Miconia calvescens)
Nicknamed the “green cancer”, miconia was brought as an ornamental plant in the 1960s. Its massive leaves shade out everything beneath, forming dark monocultures. With shallow roots, it increases erosion and threatens Maui’s water supply.
Today, miconia is confined to about 37,000 acres in East Maui. A single tree can produce 3 million seeds several times a year, which remain viable in soil for a decade.
What’s being done: Since 1991, MISC crews have been hand-cutting and herbiciding miconia across East Maui, aided by helicopter surveys. The priority is to prevent fruiting trees and keep the weed out of West Maui and higher watersheds.
How to help:
- Report sightings to 643-PEST or MISC (808-573-6472).
- Learn to recognize it: large leaves, green on top and purple underneath with three prominent veins.
- Avoid tracking seeds on boots or gear.
Strawberry Guava (Psidium cattleianum)
Brought to Hawaiʻi in 1825 for its fruit, strawberry guava now chokes out native forests, reduces groundwater recharge, and breeds fruit flies that attack agriculture. On Maui, it is widespread in East Maui and Central forests, though we see it in West Maui, Upcountry, and around most of Maui.
What’s being done: Manual clearing helps in key watershed zones, but the biggest breakthrough has been a biocontrol scale insect released in recent years that slows guava growth. Drones are now used to distribute these insects in remote forests.
How to help:
- Don’t plant or spread strawberry guava.
- Volunteer for forest restoration projects that remove guava.
- Support biocontrol programs through awareness and advocacy.
Fireweed (Senecio madagascariensis)
With its cheerful yellow flowers, fireweed looks harmless. But it’s toxic to cattle, horses, and goats, causing liver damage and death. It has spread across Maui’s pastures and fallow fields, particularly Upcountry and Central Maui.
What’s being done: A biocontrol moth (Secusio extensa) was released in 2013; its caterpillars eat fireweed leaves, helping slow its spread. Ranchers also use herbicide and better pasture management to keep it in check.
How to help:
- Ranchers can get guidance from UH CTAHR Cooperative Extension.
- Avoid moving soil or hay that might contain seeds.
- Report new infestations on islands where it isn’t widespread to 643-PEST.
Albizia (Falcataria moluccana)
Introduced in 1904, albizia is one of the fastest-growing trees on Earth, reaching 150 feet tall. Its brittle wood makes it dangerous, limbs and whole trees can fall without warning, crushing homes and power lines. Think “Widow Makers.”
On Maui, albizia is established in parts of East and West Maui. While not as dominant as on Hawaiʻi Island, it poses a growing risk.
What’s being done: Utilities and agencies remove high-risk trees near roads and power lines. Landowners are urged to eliminate young trees before they become giants. The “hack-and-squirt” herbicide method allows potentially safe killing of large trees in place.
How to help:
- Report dangerous albizias on public lands to Maui County or DLNR.
- Remove saplings on your property early.
- Never plant albizia, choose native shade trees instead.
Hookweed (Hypnea musciformis)
This invasive red seaweed was introduced illegally in the 1970s for aquaculture. On Maui, it forms massive blooms that smother coral reefs and wash up on beaches, where rotting piles deter tourists and cost millions in cleanup.
What’s being done: Agencies use manual cleanups and grazer urchins in some areas. Community beach cleanups have been critical. Researchers are exploring biocontrol and sustainable uses for the harvested algae.
How to help:
- Report large algal blooms to DAR Maui (808-243-5294) or 643-PEST.
- Join beach cleanups when blooms occur.
- Rinse gear to avoid transporting algae between snorkel/dive sites.
Small Indian Mongoose (Urva javanica)
Introduced in 1883 to control rats in sugarcane, mongooses are now a major predator of native birds, seabird nests, and turtle hatchlings. They’re widespread on Maui and impossible to eradicate island-wide. Another brilliant human plan… Now we have rats at night and mongooses during the day, splitting each day without conflict.
What’s being done: Trapping programs protect seabird colonies and turtle nesting sites. The focus statewide is preventing mongooses from reaching Kauaʻi and Lānaʻi, where they’re not established yet.
How to help:
- Report mongoose sightings only on islands where they aren’t established (Kauaʻi, Lānaʻi) at 643-PEST.
- On Maui, secure poultry and trash to avoid attracting them.
- Support seabird and turtle conservation projects that manage predators.
How You Can Make a Difference
Invasive species are one of the biggest threats to Maui’s environment, agriculture, and way of life. The good news is that everyone can help:
- Report unusual pests through Hawaiʻi’s statewide hotline at 643-PEST or 643pest.org
- Volunteer with groups like the Maui Invasive Species Committee (MISC), watershed partnerships, and community beach cleanups.
- Practice prevention: clean gear and vehicles, avoid planting invasives, and stay informed.
- Every call, every volunteer day, and every pair of watchful eyes helps protect Maui’s forests, reefs, and farms for future generations.
