Does rat birth control work?
NYC tried it in Bryant Park.
It failed. Here's why — and what's different.
The Gothamist headline was accurate: the Bryant Park pilot didn't work. The same mechanism deployed in two independent urban buildings over five months produced 79% reduction in rodent track presence. The mechanism isn't what failed. The deployment structure failed. Here's exactly what the difference is.
Why Bryant Park failed
The deployment structure was wrong before the bait went in.
The Bryant Park pilot used liquid ContraPest in an open public space. NYC rats have arguably the most abundant competing food supply of any urban rat population on earth. Without containerized trash and a prior knockdown reducing the existing population, the rats had no reason to consume the bait at the concentration needed to affect reproduction.
This is the same failure pattern across every documented negative result: standalone deployment, outdoor or open environment, active population still present, competing attractants, no monitoring to confirm the bait was even being consumed. In that structure, the product can't do what it's designed to do.
The mechanism — reducing reproductive output so the population can't replace itself at the rate it's removed — is sound biology. What it requires is a controlled enough environment for rats to consume the bait consistently. A managed bait station program inside an urban building, deployed after a knockdown phase, is that environment.
No Phase 1 knockdown
The existing population was at full density when the bait went in. Fertility management is designed to stop the replacement colony from forming — not to reduce a population that's already established at baseline.
Open outdoor environment
Bryant Park is an open space with unrestricted food access from surrounding streets, trash, and visitor activity. Managed bait stations in enclosed urban buildings produce a fundamentally different consumption pattern.
Competing attractants
NYC rats had abundant alternatives to the bait. Without containerized waste, the bait competed with the city's normal food supply rather than being the primary available option.
No monitoring
Without track count monitoring, there was no way to confirm whether consumption was occurring at the levels needed, or to adjust placement and replenishment.
What the field data shows
Two independent urban building deployments. Five months. Both produced positive results.
SenesTech published field results from two independent urban deployments in February 2026. Both used Evolve in managed bait stations, deployed after a Phase 1 knockdown, with monthly track count monitoring.
79%
reduction in rodent track presence
Location A — percentage of monitored stations showing zero activity by month 5
88%
drop in track density
Location A — tracks per monitoring plate declined even at stations with residual activity
50%+
reduction in track presence
Location B — independent urban site, same 5-month period, different site profile
Two independent sites producing positive outcomes over the same period gives the data more weight than a single result. The mechanism isn't site-specific. The biology is consistent across urban environments — what matters is deployment structure.
Source: SenesTech, Inc. — February 18, 2026
Additional deployments — June 2025
Independent deployments in Hong Kong and San Francisco produced consistent results: sightings fell within three months, bait consumption declined as the population shrank, and no new litters were detected. Different cities, different building types, same deployment structure, same direction of outcome.
Source: SenesTech, Inc. — June 26, 2025
What makes deployment succeed
Four things that separate the programs that work from the ones that don't.
Phase 1 knockdown first
The fertility management layer starts from a documented clean baseline after a knockdown clears the active population. This is what gives the bait a role: stop the replacement from forming, not reduce what's already at full density.
Managed bait stations
Stations placed along confirmed travel paths and near entry points, checked and replenished monthly. Rats are creatures of habit — managed stations along their established routes produce reliable consumption. Scattered bait in an open environment doesn't.
Urban enclosed environment
A building or property perimeter limits competing food sources to a manageable level. An open city park or outdoor space with unrestricted food access is a structurally different problem.
Monthly track count monitoring
Tracking plates at each station confirm activity is declining month over month. Monitoring shows whether the program is working and documents the trend — which is also the record you hand to an inspector.
ContraPest vs. Evolve
Same maker. Different formulations. Different deployment contexts.
Both ContraPest and Evolve are made by SenesTech. The Bryant Park pilot and NYC's current city program use ContraPest liquid. The program Cloakd deploys uses Evolve solid soft bait.
ContraPest (liquid)
Liquid formulation requiring specialized dispensers
Used in Bryant Park pilot (failed) and NYC's current Harlem program
More susceptible to competing liquid attractants in open environments
Better suited to city-scale infrastructure programs
Evolve (solid soft bait)
Solid soft bait made from cottonseed, EPA minimum risk (25b)
Deployed in standard bait stations along rat travel paths
Used in the two urban deployments that produced the 79%/88% data
Adopted by Baltimore for citywide rodent program (2025)
Available on consumer market — but deployment structure is what produces results
The structure is what makes it work.
The 90-day program runs Phase 1 knockdown through your existing exterminator, then deploys Evolve with monthly monitoring. Tell us about your property and we'll put together the outline.