Mothballs, which contain either naphthalene or paradichlorobenzene, are toxic to all species. Toxicity may occur whether the mothballs are ingested, if the chemicals are absorbed through the skin, or if the chemical vapors are inhaled. Of note, paradichlorobenzene is considered less toxic than naphthalene (found in older mothball formulations).

Mothballs

Signs and symptoms of toxicity: Clinical signs of toxicity include severe vomiting, diarrhea, refusal to eat, lethargy, loss of balance, tremors or seizures. Hemolytic anemia, liver damage, renal damage, or death can occur.

Toxic consumption:
In dogs, ingestion of 1.5 g/kg (0.6 g/lb) of naphthalene mothballs can cause hemolytic anemia. For reference, mothballs typically weigh 2.7-4g each. There is no established threshold for toxicity for cats. There is also no known toxic threshold for paradichlorobenzene ingestion. All incidents of exposure should be reported immediately.

Dogs: Naphthalene Mothball Toxic Consumption
X-Small
Yorkie, Chihuahua
Small
Pug, Boston Terrier, Poodle
Medium
Beagle, Scottish Terrier
Large
Boxer, Cocker Spaniel
X-Large
Retriever, German Shepherd
XX-Large
Great Dane, St. Bernard
1 – 10 lbs.
(0.45 – 4.6 kg)
11 – 25 lbs.
(5 – 11.4 kg)
26 – 40 lbs.
(11.8 – 18.2 kg)
41 – 70 lbs.
(18.6 – 31.8 kg)
71 – 90 lbs.
(32.3 – 40.9 kg)
91 – 110 lbs.
(41.4 – 50 kg)
dog1 dog2 dog3 dog4 dog7 dog6
> 0.6 g
(~ 0.25 mothballs)
> 7.5 g
(~ 2.5 mothballs)
> 17 g
(~ 6.5 mothballs)
> 27 g
(~ 10 mothballs)
> 48 g
(~ 17 mothballs)
> 62 g
(~ 23 mothballs)

 

References:
Osweiler, G, et al. (2011). Blackwell’s five-minute veterinary consult clinical companion. Small Animal Toxicology. [Kindle version]. Retrieved from Amazon.com