A host of events that conspired to spook investors in May, from a “flash crash” to debt woes in Europe and the threat of war between North and South Korea. While millions of investors took comfort in exchange traded funds (ETFs) that cover safe-haven asset classes, it wasn’t enough to send assets higher for the month.

Assets in U.S.-listed exchange traded funds (ETFs) and exchange traded notes (ETNs) totaled approximately $798 billion at the end of May, an increase of almost 34% over May 2009, when assets totaled $594.3 billion. It marks a 6% decline from assets at the end of April.

Bear ETFs nabbed a hefty chunk of inflows last month, taking in a total of nearly $1.3 billion for the month.

May closed the month with the number of listed products totaling 995, compared to 829 listed products at the end of May 2009. In April, the U.S. ETF industry crossed the 1,000 ETF mark, but stepped back this month as a result of some closures. Several ETFs have already launched this month, so the industry won’t remain below 1,000 for long. [Check Out Our May ETF Performance Report.]

Dave Nadig and Oliver Ludwig for Index Universe report that investors fled riskier assets and piled into safer havens such as gold and Treasury bond funds. The single-biggest winning fund was the State Street Global Advisors SPDR Gold Trust (NYSEArca: GLD), which added $4.22 billion in assets, bringing the total to $49.21 billion, as fiscal problems in Europe escalated.

Another winner last month was PIMCO Enhanced Short Maturity Strategy Fund (NYSEArca: MINT), which gathered $596.4 million in assets.

For more stories about performance, visit our performance reports category.

Tisha Guerrero contributed to this article.

The opinions and forecasts expressed herein are solely those of Tom Lydon, and may not actually come to pass. Information on this site should not be used or construed as an offer to sell, a solicitation of an offer to buy, or a recommendation for any product.