Cited from endi.com
"The mongoose Herpestes javanicus) was introduced in Puerto Rico in the late 20th century, to fight rats in cane plantations, and it's considered responsible for the decrease in the Puerto Rican boa numbers." Nevertheless, mongooses are terrestrial and diurnal animals, whereas boas are mainly nocturnal and arboreal – as well as the rats the mongoose was supposed to fight-, "although it is possible to see them sun bathing on the ground during the morning, or before arriving to its daytime hiding place."
"Encounters between the two species cannot be frequent, and none of the studies of the mongoose’s stomach content has revealed remains of boas or any other snake."
Since 1930’s the shortage of boas has been attributed to the mongoose. Recently some articles have proposed that the mongoose is responsible for the extinction of at least seven species of amphibians and reptiles in Puerto Rico and the Caribbean.
However "if looked for in the appropriate places and with enough intensity, the boa is anything but scarce, as demonstrated by doctor Sandra Moya, who collected 41 boas in 46 days, five in one day, or the sighting of 14 to 16 boas by doctor Fernando Bird in a cave in Arecibo."
"It can be argued that the boa was scarce, and the population has been reconstituted recently, but if this was the case, it has to be accepted that it did it in spite of the mongoose."
"Also, one could ask how is it possible that the mongoose, well known as a predator for birds and reptiles, allowed the reproduction of the iguana (Iguana iguana) in Puerto Rico, whose eggs and flesh should be a treat for the voracious appetite of the mongoose."
The case of the mongoose and the Puerto Rican boa, as well as the case of the coqui as an invading species in Hawaii, seem to be an exception to the ecologists assertion that invasions are the illness of the ecosystem.