After Flaco was found dead earlier this year with rat poison in his system (and an apparent case of pigeon herpes), Councilmember Shaun Abreu introduced a bill named for the Eurasian owl that would pilot the use of contraceptives instead of rodenticides to help control the city’s rat problem. (Rat poison also played a role in the death of Barry, another celebrity owl.) In the proposed pilot, pellets would be spread in a series of ten-block zones around the city and have their efficacy tracked over the course of a year. The rats will apparently eat these pellets because, according to Dr. Loretta Mayer, the co-founder of SenesTech and the scientist behind the product Abreu focused on in his proposal, they taste “better than pizza.”
The bill might be something rat haters and rat lovers can get behind, but the city has tried rat contraceptives before and the rats are, well, still here. (An attempt to use a liquid contraceptive in Bryant Park last year was deemed a failure by the Bryant Park Corporation.) So what’s going to happen this time? We reached out to Michael H. Parsons, a rodentologist and former Fordham University researcher, about the science behind rat contraceptives, the tricky matter of tracking their effectiveness, how to measure success, and rat cognition and ticklishness.
This interview has been edited and condensed for clarity.
How do these rat contraceptives work?
It makes them sterile by depleting all stages of ovarian follicles in the female and disrupting spermatogenesis in the male.
So the rats are done reproducing.
Correct.
And they’re safe for other animals?
SenesTech claims contraceptives will not harm other species. Apparently it’s got a very short half-life, so it’s metabolized very quickly. So an animal that consumes a rat that has died while having the contraceptives in its system is not going to have any effects. That’s the idea.
So previous tries in the city have had underwhelming results. Does this stuff work?
They’ve shown in laboratory studies that when an animal consumes this, it certainly has a wonderful effect on them — wonderful as in having the targeted impact. But I’ve been arguing that the city needs to sponsor the proper data-driven trials of many different products, this being one of them. There have been trials of contraceptives in New York and they had mixed results. And the reason was because it’s so difficult to generate good data on whether a rat is reproducing or not. So it is tricky. I’ve just sort of hoped we would not put the cart before the horse and roll these things out until we have some data suggesting that they have some efficacy.
So you would have to follow what happens to a rat after they eat the pellet?
Yes. There are several “response variables” that could be quantified. Firstly, they need to work on a smaller scale in isolated populations of rats to show that rats — and not some other animal — are actually consuming the bait. Next, they need to determine the proportion of a population that is consuming — if 100 percent of rats are not consuming, then we have a problem. Then we need to find ways to determine if the bait is having an impact on the number of rats being born. We assume it works as it did in the laboratory, but it only takes a single pair of rats to show otherwise.
Why would something as small as that have such a wide-ranging impact?
I actually did write to both Loretta Mayer and Cheryl Dyer, who founded the company, and I said, “All it takes is one, just a single rodent.” All it takes is one rodent not to like the taste of the liquid. I said we need to find some other delivery mechanisms. With the pellets you sort of have the same issue in that the animal has to voluntarily consume it. Say the animal doesn’t particularly like the taste — if this animal has offspring and the other animals that like the taste don’t have offspring, how many generations is it going to be until the new genotype takes over and displaces the old genotype? That’s the tricky thing about this.
And rats reproduce pretty quickly.
One rat can have up to 12 pups at one time. Each rat, within six to eight weeks, could be sexually mature and produce up to 12 of their own. That’s the extreme example of where there’s no competition and food available. But as you can see, you could have an enormous amount of rats.
The scientists who made them say these pellets have a lot of fat and salts that are delicious to rats.
Like anything, if it’s better than what’s around, then sure. But I always want to see the data. One is the uptake. Will the animals eat it? We have that for the lab rats, but we don’t have that for wild animals. And how many of the wild animals prefer them? Rats will eat typically what’s around them. So in Brooklyn I would use pizza and beer to attract rats. And if I am in some other place that throws out a lot of scraps of a particular food, then those animals will actually prefer that because that’s what they trust. So fats and salts sound great in theory, but I want to know if the animals agree.
Are there certain situations where these contraceptives might work best?
I’ve always felt that contraceptives are wonderful to work as an adjunct with other approaches on the local scale. They could be in situations where the flow of genes is restricted — in other words, where there’s one group of animals and no other animals are moving in and out. That could be in particularly isolated areas of the subway or particularly isolated areas in apartments inside residences. But if you’re talking about doing this on a block-wide level, there’s so much movement between populations that I think it remains to be seen.
So it sounds like rats are really variable, and really adaptable — so we need to know what happens in an actual real-life scenario.
I’ll give you an example from a few years back. When he was mayor, Bill de Blasio declared war on rodents. His bill included funding $5 million worth of mint-scented garbage bags. It was true that if rats can smell food from one bag and not another, they would choose the one without the scent. But as soon as rat food was limited what ended up happening over time was the rats sought out mint scents because behind the veil was a smorgasbord of food. It became kind of like this Pavlovian thing. “Now mint scent makes me salivate because I know that there’s food available.” That was the silliest thing ever.
So is a pilot worth it?
I am pleased that they’re going to do a pilot study. But I can tell you from being a researcher that getting that data is an enormous undertaking. I’m curious who is actually doing that work and how they intend to do it. They should do it in conjunction with rodentologists. It would be nice to have some localized trials on a smaller scale in a restricted context showing that it’s working first — instead of ten-block areas, let’s do one block or two blocks. How do we go onto a ten-block area and say, “Ah, it’s the contraceptives working,” and not something else that’s having the effect? I would want to make sure there’s hard data coming out of it because there’s nothing I loathe more than anecdotes. You might as well use Amazon reviews.
The city councilmember behind the effort said that past attempts in New York have failed in part because the contraceptives weren’t paired with containerization.
When they’re saying the problem is they didn’t use it with a containerization — well, the whole point of contraceptives is it’s got to have some efficacy on its own or we’re never going to know that we’re spending our money on something that can be useful. Even if you were to show me a 10 or 20 percent reduction without the containerization, that means something to me.
What about the poisons — are those proven to work better?
I’ve actually argued that we don’t really have the evidence we need to show that rodenticides work enough to take the risks that we’re taking with non-target uptake. But these have been on the market for so many decades. What we can see are the animals are suffering a lot. We know rats are suffering. It’s just excruciating how this anticoagulant causes the animal to suffer for a few days before it actually dies.
It’s a little gruesome. Animal advocates obviously hate them. PETA is doing a whole “rats have rights” campaign. What do you think about this?
I’ve spent a lot of time catching, releasing, and interacting with rats while they’re in their cages. Some of them would even come up behind me and hang around while I did my research. I found that these rats are incredibly sentient. They had an awareness about them, they had an intelligence about them. From what we’re hearing, even the rats inside laboratories are sentient enough that they are foregoing a chocolate reward to save another rat from drowning. Now we have trials of rats that are driving little robot cars.
Oh my gosh.
It’s sort of cute, but it also drives home the point. And wild rats are so much more intelligent than lab rats. We know they experience mourning and sadness and joy. We’re learning that rats are ticklish. They giggle and they express what we would think of as joy at these higher frequencies. And as we learn more, we’re learning that these animals are not the bogeyman. I now see us as the bogeyman and not the rats because rats are a reflection of us. Where we are clean, there are no rats. Where we throw pizza down, we’re going to have Pizza Rat. So I agree with PETA on that perspective.
Is containerization, then, the main solution?
Yes, assuming containerization means proper pickup and removal. Because I’ve seen some of the big containers out on Riverside and they were full and people were just throwing stuff outside. They were overflowing because they weren’t being serviced.
You’ve worked in this field a long time and you’ve seen this before — as you said, de Blasio declared a war on rats and now Adams has declared a war on rats. How do you think the city is actually doing now? Where are we on this arc of trying to actually solve the problem?
We’re making so much progress. We were at about two out of ten with de Blasio, and I would say since the rat czar came on board, we’re up to around a six. The reason for the higher grade is partly because the czar position has helped centralize rodent control as opposed to the old administration spreading it out among many levels of city government — none of whom were coordinated with the other. We’ve got a long way to go, but we’ve made some leaps.