diff --git a/scrapy/contrib/spiders/sitemap.py b/scrapy/contrib/spiders/sitemap.py
index 91ae78c62..f96367905 100644
--- a/scrapy/contrib/spiders/sitemap.py
+++ b/scrapy/contrib/spiders/sitemap.py
@@ -22,7 +22,7 @@ class SitemapSpider(BaseSpider):
         self._follow = [regex(x) for x in self.sitemap_follow]
 
     def start_requests(self):
-        return [Request(x, callback=self._parse_sitemap) for x in self.sitemap_urls]
+        return (Request(x, callback=self._parse_sitemap) for x in self.sitemap_urls)
 
     def _parse_sitemap(self, response):
         if response.url.endswith('/robots.txt'):
diff --git a/scrapy/spider.py b/scrapy/spider.py
index cb090e3db..1829a9d3b 100644
--- a/scrapy/spider.py
+++ b/scrapy/spider.py
@@ -50,10 +50,8 @@ class BaseSpider(object_ref):
         return self._settings
 
     def start_requests(self):
-        reqs = []
         for url in self.start_urls:
-            reqs.extend(arg_to_iter(self.make_requests_from_url(url)))
-        return reqs
+            yield self.make_requests_from_url(url)
 
     def make_requests_from_url(self, url):
         return Request(url, dont_filter=True)